Double patterning process

ABSTRACT

Double patterns are formed by coating a first chemically amplified positive resist composition comprising an acid labile group-bearing resin and a photoacid generator and prebaking to form a resist film on a processable substrate, exposing the resist film to high-energy radiation, PEB, and developing with an alkaline developer to form a first positive resist pattern, treating the first resist pattern to be alkali soluble and solvent resistant, coating a second resist composition and prebaking to form a reversal film, and exposing the reversal film to high-energy radiation, PEB, and developing with an alkaline developer to form a second positive resist pattern. The last development step includes dissolving away the reversed first resist pattern and achieving reversal transfer.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2008-032668 filed in Japan on Feb. 14, 2008, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a double patterning process for forming a first pattern of reversal transfer and a second positive pattern simultaneously in an overlapping manner, involving the steps of forming a positive pattern through exposure and development, and heat or otherwise treatment for converting the positive pattern to be alkali soluble, coating a second positive resist composition as a reversal film-forming composition thereon, and forming a second positive pattern through exposure, bake and development, wherein the first pattern which has been converted to be alkali soluble can be removed at the same time as the last development.

BACKGROUND ART

In the recent drive for higher integration and operating speeds in LSI devices, the pattern rule is made drastically finer. The photolithography which is currently on widespread use in the art is approaching the essential limit of resolution determined by the wavelength of a light source. As the light source used in the lithography for resist pattern formation, g-line (436 nm) or i-line (365 nm) from a mercury lamp was widely used in 1980's. Reducing the wavelength of exposure light was believed effective as the means for further reducing the feature size. For the mass production process of 64 MB dynamic random access memories (DRAM, processing feature size 0.25 μm or less) in 1990's and later ones, the exposure light source of i-line (365 nm) was replaced by a KrF excimer laser having a shorter wavelength of 248 nm. However, for the fabrication of DRAM with a degree of integration of 256 MB and 1 GB or more requiring a finer patterning technology (processing feature size 0.2 μm or less), a shorter wavelength light source was required. Over a decade, photolithography using ArF excimer laser light (193 nm) has been under active investigation. It was expected at the initial that the ArF lithography would be applied to the fabrication of 180-nm node devices. However, the KrF excimer lithography survived to the mass-scale fabrication of 130-nm node devices. So, the full application of ArF lithography started from the 90-nm node. The ArF lithography combined with a lens having an increased numerical aperture (NA) of 0.9 is considered to comply with 65-nm node devices. For the next 45-nm node devices which required an advancement to reduce the wavelength of exposure light, the F₂ lithography of 157 nm wavelength became a candidate. However, for the reasons that the projection lens uses a large amount of expensive CaF₂ single crystal, the scanner thus becomes expensive, hard pellicles are introduced due to the extremely low durability of soft pellicles, the optical system must be accordingly altered, and the etch resistance of resist is low; the postponement of F₂ lithography and the early introduction of ArF immersion lithography were advocated (see Proc. SPIE Vol. 4690 xxix).

In the ArF immersion lithography, the space between the projection lens and the wafer is filled with water. Since water has a refractive index of 1.44 at 193 nm, pattern formation is possible even using a lens having a numerical aperture (NA) of 1.0 or greater. Theoretically, it is possible to increase the NA to nearly 1.44. It was initially recognized that the resolution could be degraded and the focus be shifted by a variation of water's refractive index with a temperature change. The problem of refractive index variation could be solved by controlling the water temperature within a tolerance of 1/100° C. while it was recognized that the impact of heat from the resist film upon light exposure drew little concern. There was a likelihood that micro-bubbles in water could be transferred to the pattern. It was found that the risk of bubble generation is obviated by thorough deaeration of water and the risk of bubble generation from the resist film upon light exposure is substantially nil. At the initial phase in 1980's of the immersion lithography, a method of immersing an overall stage in water was proposed. Later proposed was a partial-fill method of using a water feed/drain nozzle for introducing water only between the projection lens and the wafer so as to comply with the operation of a high-speed scanner. In principle, the immersion technique using water enabled lens design to a NA of 1 or greater. In optical systems based on traditional refractive index materials, this leads to giant lenses, which would deform by their own weight. For the design of more compact lenses, a catadioptric system was proposed, accelerating the lens design to a NA of 1.0 or greater. A combination of a lens having NA of 1.2 or greater with strong resolution enhancement technology suggests a way to the 45-nm node (see Proc. SPIE, Vol. 5040, p724). Efforts have also been made to develop lenses of NA 1.35.

One candidate for the 32-nm node lithography is lithography using extreme ultraviolet (EUV) radiation with wavelength 13.5 nm. The EUV lithography has many accumulative problems to be overcome, including increased laser output, increased sensitivity, increased resolution and minimized line-edge roughness (LWR) of resist coating, defect-free MoSi laminate mask, reduced aberration of reflection mirror, and the like.

The water immersion lithography using a NA 1.35 lens achieves an ultimate resolution of 40 to 38 nm at the maximum NA, but cannot reach 32 nm. Efforts have been made to develop higher refractive index materials in order to further increase NA. It is the minimum refractive index among projection lens, liquid, and resist film that determines the NA limit of lenses. In the case of water immersion, the refractive index of water is the lowest in comparison with the projection lens (refractive index 1.5 for synthetic quartz) and the resist film (refractive index 1.7 for prior art methacrylate-based film). Thus the NA of projection lens is determined by the refractive index of water. Recent efforts succeeded in developing a highly transparent liquid having a refractive index of 1.65. In this situation, the refractive index of projection lens made of synthetic quartz is the lowest, suggesting a need to develop a projection lens material with a higher refractive index. LuAG (lutetium aluminum garnet Lu₃Al₅O₁₂) having a refractive index of at least 2 is the most promising material, but has the problems of birefringence and noticeable absorption. Even if a projection lens material with a refractive index of 1.8 or greater is developed, the liquid with a refractive index of 1.65 limits the NA to 1.55 at most, failing in resolution of 32 nm despite successful resolution of 35 nm. For resolution of 32 nm, a liquid with a refractive index of 1.8 or greater and resist and protective films with a refractive index of 1.8 or greater are necessary. Among the materials with a refractive index of 1.8 or greater, the high refractive index liquid seems least available. Such a liquid material has not been discovered because a tradeoff between absorption and refractive index is recognized in the art. In the case of alkane compounds, bridged cyclic compounds are preferred to linear ones in order to increase the refractive index, but the cyclic compounds undesirably have too high a viscosity to follow high-speed scanning on the exposure tool stage. If a liquid with a refractive index of 1.8 is developed, then the component having the lowest refractive index is the resist film, suggesting a need to increase the refractive index of a resist film to 1.8 or higher.

The process that now draws attention under the above-discussed circumstances is a double patterning process involving a first set of exposure and development to form a first pattern and a second set of exposure and development to form a pattern between features of the first pattern. See Proc. SPIE, Vol. 5754, p 1508 (2005). A number of double patterning processes are proposed. One exemplary process involves a first set of exposure and development to form a photoresist pattern having lines and spaces at intervals of 1:3, processing the underlying layer of hard mask by dry etching, applying another layer of hard mask thereon, a second set of exposure and development of a photoresist film to form a line pattern in the spaces of the first exposure, and processing the hard mask by dry etching, thereby forming a line-and-space pattern at a half pitch of the first pattern. An alternative process involves a first set of exposure and development to form a photoresist pattern having spaces and lines at intervals of 1:3, processing the underlying layer of hard mask by dry etching, applying a photoresist layer thereon, a second set of exposure and development to form a second space pattern on the remaining hard mask portion, and processing the hard mask by dry etching.

In either process, the hard mask is processed by two dry etchings. Both the former and latter processes require two etchings for substrate processing, leaving the issues of a reduced throughput and deformation and misregistration of the pattern by two etchings.

One method that proceeds with a single etching is by using a negative resist material in a first exposure and a positive resist material in a second exposure. Another method is by using a positive resist material in a first exposure and a negative resist material in a higher alcohol of 4 or more carbon atoms, in which the positive resist material is not dissolvable, in a second exposure. Since negative resist materials with low resolution are used, these methods entail degradation of resolution.

A method which does not involve post-exposure bake (PEB) and development between first and second exposures is the simplest method with high throughputs. This method involves first exposure, replacement by a mask having a shifted pattern drawn, second exposure, PEB, development and dry etching. However, the energy of light for second exposure offsets the energy of light for first exposure so that the contrast becomes zero, leading to a failure of pattern formation. If an acid generator capable of two photon absorption or a contrast enhancement layer (CEL) is used to provide nonlinear acid generation, then the energy offset is relatively reduced even when second exposure is performed at a half-pitch shifted position. Thus a pattern having a half pitch corresponding to the shift can be formed, though at a low contrast. See Jpn. J. Appl. Phy. Vol. 33 (1994) p 6874-6877, Part 1, No. 12B, December 1994. In this regard, if the mask is replaced on every exposure, the throughput is substantially reduced. Then first exposure is performed on a certain number of wafers before second exposure is performed. Due to acid diffusion during the standing time between the first and second exposures, there can occur dimensional variations which are of concern.

In addition to the double patterning technique, the technology for forming a fine space pattern or hole pattern includes use of negative resist, thermal flow, and RELACS. The negative resist material suffers from the problem that the resist itself has a low resolution as discussed above. The thermal flow is another process of forming a fine space pattern. The space pattern once formed is heated at a temperature above the glass transition temperature (Tg) of the resist pattern, causing the pattern to flow to narrow the spaces. The RELACS known as a further process of forming a fine space pattern is by applying on the space pattern a composition in a solvent in which the resist pattern is not soluble and adding chemical attachment by heat, thereby narrowing the space.

The method of forming a negative pattern by reversal of a positive pattern is well known from the past. For example, JP-A 2-154266 and JP-A 6-27654 disclose naphthoquinone resists capable of pattern reversal. JP-A 64-7525 describes exposure of selected portions of a film to focused ion beam (FIB) for curing and flood exposure whereby the cured portions are left behind. JP-A 1-191423 and JP-A 1-92741 describe exposure of a photosensitive agent of naphthoquinone diazide to form an indene carboxylic acid, heat treatment in the presence of a base into an indene which is alkali insoluble, and flood exposure to effect positive/negative reversal.

As to the positive/negative reversal method including exchange of developers, attempts were made to form negative patterns by development in an organic solvent of hydroxystyrene partially protected with tert-butoxycarbonyl (t-BOC) groups, and by development with super-critical carbon dioxide.

As to the positive/negative reversal method utilizing silicon-containing materials, it is proposed to form a fine hole pattern by covering a space portion of a positive resist pattern with a silicon-containing film, effecting oxygen gas etching for etching away the positive pattern portion, thus achieving positive/negative reversal to leave a silicon-containing film pattern. See JP-A 2001-92154 and JP-A 2005-43420.

All the foregoing methods based on positive/negative reversal are impractical due to process complexity and fail to form a fine pattern by further processing a pattern reversed film.

SUMMARY OF INVENTION Technical Problem

In connection with the fabrication of LSIs which are advancing toward higher integration and operating speeds, double patterning is proposed and reported as being able to process to a very fine pattern rule. However, the process is not simple, and is regarded rather complex as requiring first lithography, subsequent etching, second lithography, and further etching (2nd lithography and 2nd etching). There is a desire to have a technique capable of processing by a single etching after patterning by two lithography processes. However, the technique of converting the first pattern to be insoluble in an organic solvent used in the second resist composition, and improvements in the resolving performance of both the first and second resist compositions remain as important problems to be solved.

In addition to the double patterning technique, the technology for forming fine spaces is very important and includes use of negative resist, thermal flow, and RELACS. The negative resist material suffers from the problem that the resist itself has a low resolution. The thermal flow is another process of forming a fine space pattern. Because the quantity of pattern material available for flow is reduced as the feature size becomes finer, the thermal flow process becomes difficult to reserve a sufficient quantity of flow. In general, resist compositions capable of high resolution performance have a high glass transition temperature (Tg) so that a sufficient flow may not occur during the thermal flow step at a certain heating temperature. It is also said that the size reduction by thermal flow encounters a limit. The RELACS known as a further process of forming a fine space pattern is by adding chemical attachment to the space pattern by heat, thereby narrowing the space. There are problems that the amount of attachment varies depending on the type of resist composition of which spaces are formed, and variations occur during dimensional shrinkage by heat. Another potential problem is a likelihood of generating pattern defects.

In connection with the fabrication of LSIs which are advancing toward higher integration and operating speeds, there is a structure layer which requires a very fine pattern rule, especially fine space pattern. However, improving the miniaturization of only a space pattern is insufficient. Because in the same layer, there may be present an isolated line and a pattern having different pitch or different line/space ratio (duty ratio), the techniques for miniaturizing both spaces and isolated lines must be compatible. Since the factor for enhancing the resolution of spaces is utterly different from the factor for improving the resolution of isolated lines, the techniques for miniaturizing spaces and isolated lines are generally in tradeoff relationship as well as the improvement in process margin. Solving the miniaturization of spaces and isolated lines at the same time becomes more difficult as high-density integration and high-speed operation are accelerated.

On the other hand, if a positive pattern once formed at a high resolution can be reversed to be negative, a fine space pattern is obtainable. As mentioned above, a variety of methods for reversing a positive image formed of a positive resist material capable of high resolution into a negative pattern have been reported. All these methods based on positive/negative reversal are impractical due to process complexity. They fail to form a fine pattern by further processing a pattern reversed film. In the related art, only examples of reversal transfer are known while there are no examples of double patterning in which lithographic patterning is applied to a film subject to reversal transfer.

Solution to Problem

The inventors have found that when a resin in a first chemically amplified positive resist composition of which a positive resist pattern is composed is subjected to partial crosslinking treatment, the crosslinking reaction is controlled to proceed to such an extent to provide the necessary organic solvent resistance and to keep a solubility in an alkaline developer; that when a reversal film is coated thereon, a fine space pattern can be formed through positive/negative reversal by the treatment. Additionally, when the film to be coated for reversal transfer purpose is a positive resist film, the film material to which the first resist pattern is reversal transferred can be processed by lithography. This enables double patterning.

Accordingly, in a first aspect (claim 1), the invention provides a double pattern forming process comprising the steps of:

coating a first chemically amplified positive resist composition onto a processable substrate, said resist composition comprising a resin comprising recurring units having an alkali-soluble group protected with an acid labile group which is eliminatable with acid, the resin being convertible to be soluble in an alkaline developer as a result of elimination of acid labile groups, a photoacid generator capable of generating an acid upon exposure to high-energy radiation, and an organic solvent, and prebaking the resist composition to remove the unnecessary solvent to form a resist film,

exposing the resist film to high-energy radiation in a first pattern of exposed and unexposed areas, post-exposure baking for causing the acid generated by the acid generator upon exposure to act on the acid labile groups on the resin whereby the acid labile groups on the resin in the exposed area undergo elimination reaction so that the resin in the exposed area becomes alkali soluble, and developing the exposed resist film with an alkaline developer to form a first positive resist pattern,

treating the first resist pattern so as to eliminate the acid labile groups on the resin in the first resist pattern and to induce crosslinking in the resin to such an extent that the resin may not lose a solubility in an alkaline developer, for thereby endowing the first resist pattern with resistance to an organic solvent to be used in a reversal film-forming composition,

coating a reversal film-forming composition thereon to form a reversal film, said reversal film-forming composition being a second chemically amplified positive resist composition comprising a resin comprising recurring units having an alkali-soluble group protected with an acid labile group which is eliminatable with acid, a photoacid generator capable of generating an acid upon exposure to high-energy radiation, and an organic solvent, and prebaking the second resist composition to remove the unnecessary solvent to form the reversal film, and

exposing the reversal film to high-energy radiation in a second pattern of exposed and unexposed areas, post-exposure baking for causing the acid generated by the acid generator upon exposure to act on the acid labile groups on the resin whereby the acid labile groups on the resin in the exposed area undergo elimination reaction, and developing the exposed reversal film with an alkaline developer to form a second positive resist pattern,

wherein the last step of developing the exposed reversal film with an alkaline developer to form a second resist pattern includes dissolving away the first resist pattern which has been converted to be soluble in the alkaline developer and achieving reversal transfer of the first resist pattern to the second resist pattern.

The inventors have found that partial crosslinking between molecules of the resin of which the positive pattern of the first resist film is composed has a level that maintains a solubility in an alkaline developer resulting from elimination of acid labile groups and provides resistance to an organic solvent at the same time. This permits removal of the positive pattern portion in the final step of positive/negative reversal to be implemented in a very simple manner. Additionally, the film subject to reversal transfer is made of a chemically amplified positive resist composition which can be processed by lithography. This enables double patterning.

In a preferred embodiment (claim 2), in the step of exposing, baking and developing to form a second resist pattern, exposure to the second pattern is performed between features of the first pattern to define the second resist pattern of spaces which are removable by alkaline development and located between spaces in the pattern resulting from reversal transfer of the first resist pattern, whereby repetitive patterns of lines and spaces are formed on the processable substrate.

Then, fine lines and spaces can be formed (or patterned) on the processable substrate by two lithography steps. Since this need be followed by a single etching only, a simplified double patterning process is provided.

In a preferred embodiment (claim 3), in the step of exposing, baking and developing to form a second resist pattern, exposure to the second pattern is performed at a position spaced apart from the first resist pattern, whereby the second resist pattern is formed on the processable substrate apart from the pattern resulting from reversal transfer of the first resist pattern.

This embodiment also provides a simplified double patterning process involving two lithographic steps to form patterns on the processable substrate and subsequent single etching. In the single patterning process (involving a single exposure step for patterning), improving the process margins of a fine space pattern, and a pattern having an isolated line or different pitch or different line/space ratio (duty ratio) is believed quite difficult because of their tradeoff relationship. The double patterning process of the invention enables to improve both the process margins. That is, the reversed first resist pattern enables resolution of fine spaces, and a pattern having mixed isolated lines or different pitch or different line/space ratio (duty ratio) can be formed from the second positive resist composition. This leads to the advantage of improving the process margins of both the patterns.

The double patterning process of the invention enables to form a variety of patterns by reducing the pitch between pattern features, or by two exposure steps of intersecting patterns and positive/negative reversal of the first pattern. For example, a crisscross hole pattern and a pattern of holes with very thin walls therebetween can be formed in preferred embodiments (claims 4 to 6).

In a preferred embodiment (claim 7) for implementing the step of forming a first resist pattern, the first chemically amplified positive resist composition comprises a resin comprising recurring units having a lactone ring and recurring units of alicyclic structure having an alkali-soluble group protected with an acid labile group which is eliminatable with acid. While the lactone ring structure is known to impart adhesion to the resist film, the resin comprising such units is advantageously used in crosslink formation in the step of endowing the resin with organic solvent resistance.

In a preferred embodiment (claim 8), the first chemically amplified positive resist composition comprises a resin comprising recurring units having a 7-oxanorbornane ring and recurring units having an alkali-soluble group protected with an acid labile group of alicyclic structure which is eliminatable with acid, and the step of treating the first resist pattern so as to eliminate the acid labile groups on the resin in the first resist pattern is performed by heating whereby elimination of acid labile groups and crosslinking of the resin simultaneously take place. The 7-oxanorbornane ring advantageously serves to impart organic solvent resistance.

In a preferred embodiment (claim 9), the recurring units having a 7-oxanorbornane ring are recurring units having the general formula (a).

Herein R¹ is hydrogen or methyl, R² is a single bond or a straight, branched or cyclic C₁-C₆ alkylene group which may have an ether or ester group, and which has a primary or secondary carbon atom through which it is linked to the ester moiety in the formula, R³, R⁴ and R⁵ are each independently hydrogen or a straight, branched or cyclic C₁-C₆ alkyl group, and “a” is a number in the range: 0<a<1.0.

In a preferred embodiment (claim 10), the recurring units having an alkali-soluble group protected with an acid labile group which is eliminatable with acid are recurring units having the general formula (b):

Herein R⁶ is hydrogen or methyl, R⁷ is an acid labile group, and b is a number in the range: 0<b≦0.8. The inclusion of units of the illustrated structure ensures that the dissolution rate is readily increased by reaction with acid, improving the resolution performance of the first resist film and facilitating removal with the alkaline developer of the second resist film serving as the film subject to reversal transfer.

In a preferred embodiment (claim 11), the second chemically amplified positive resist composition comprises a resin comprising recurring units having a lactone ring and recurring units having an alkali-soluble group protected with an acid labile group which is eliminatable with acid. The lactone ring structure functions to impart adhesion to the second resist film as in the case of the first resist film.

In a preferred embodiment (claim 12) of the second chemically amplified positive resist composition, the recurring units having an alkali-soluble group protected with an acid labile group which is eliminatable with acid are recurring units having the general formula (c).

Herein R⁸ is hydrogen or methyl, R⁹ is an acid labile group, and c is a number in the range: 0<c≦0.8.

In a preferred embodiment (claim 13) of the second chemically amplified positive resist composition, the resin comprising recurring units having an alkali-soluble group protected with an acid labile group which is eliminatable with acid is a polysiloxane compound.

In a preferred embodiment (claim 14), the polysiloxane compound comprises structural units having the general formulae (1) and (2) and further comprises third structural units having the general formula (3).

Herein R¹⁰ is a C₃-C₂₀ monovalent organic group of straight, branched, cyclic or polycyclic structure which has a hydroxyl group on a carbon atom as a functional group, which has in total at least three fluorine atoms substituted on the carbon atoms bonded to the hydroxyl-bonded carbon atom, and which may contain a halogen, oxygen or sulfur atom in addition to the fluorine atoms; R¹¹ is a C₁-C₆ monovalent hydrocarbon group of straight, branched or cyclic structure; R¹² is a C₃-C₂₀ monovalent organic group of straight, branched, cyclic or polycyclic structure which has a carboxyl group protected with an acid labile protective group as a functional group, and which may contain a halogen, oxygen or sulfur atom in addition to the carboxyl group; R¹³ is as defined for R¹¹; R¹⁴ is a C₄-C₁₆ monovalent organic group which has a lactone ring as a functional group and which may contain a halogen, oxygen or sulfur atom in addition to the lactone ring; R¹⁵ is as defined for R¹¹; p is 0 or 1, q is 0 or 1, and r is 0 or 1.

In a preferred embodiment (claim 15), the step of treating the first resist pattern for endowing the first resist pattern with resistance to an organic solvent to be used in a reversal film-forming composition includes heating at a higher temperature than in the prebaking and PEB steps.

Typically, ArF immersion lithography is used in the pattern forming process of the invention. In the ArF immersion lithography, water is generally used as the liquid, and it is a common practice to use a protective coating for preventing the acid from being leached out in water.

A pattern forming process using a protective coating is also contemplated herein. A further embodiment of the invention (claim 16) is a double pattern forming process comprising the steps of:

coating a first chemically amplified positive resist composition onto a processable substrate, said resist composition comprising a resin comprising recurring units of the structure having an alkali-soluble group protected with an acid labile group which is eliminatable with acid, the resin being convertible to be soluble in an alkaline developer as a result of elimination of acid labile groups, a photoacid generator capable of generating an acid upon exposure to high-energy radiation, and an organic solvent, and prebaking the resist composition to remove the unnecessary solvent to form a resist film,

coating a protective film-forming composition onto the resist film and heating to remove an unnecessary solvent to form a protective film,

exposing the resist film to high-energy radiation in a first pattern of exposed and unexposed areas, post-exposure baking for causing the acid generated by the acid generator upon exposure to act on the acid labile groups on the resin whereby the acid labile groups on the resin in the exposed area undergo elimination reaction so that the resin in the exposed area becomes alkali soluble, and developing the exposed resist film with an alkaline developer to form a first positive resist pattern,

treating the first resist pattern so as to eliminate the acid labile groups on the resin in the first resist pattern and to induce crosslinking in the resin to such an extent that the resin may not lose a solubility in an alkaline developer, for thereby endowing the first resist pattern with resistance to an organic solvent to be used in a reversal film-forming composition,

coating a reversal film-forming composition thereon to form a reversal film, said reversal film-forming composition being a second chemically amplified positive resist composition comprising a resin comprising recurring units of the structure having an alkali-soluble group protected with an acid labile group which is eliminatable with acid, a photoacid generator capable of generating an acid upon exposure to high-energy radiation, and an organic solvent, and prebaking the second resist composition to remove the unnecessary solvent to form the reversal film,

coating a protective film-forming composition onto the reversal film and heating to remove an unnecessary solvent to form a protective film, and

exposing the reversal film to high-energy radiation in a second pattern of exposed and unexposed areas, post-exposure baking for causing the acid generated by the acid generator upon exposure to act on the acid labile groups on the resin whereby the acid labile groups on the resin in the exposed area undergo elimination reaction, and developing the exposed reversal film with an alkaline developer to form a second positive resist pattern,

wherein the last step of developing the exposed reversal film with an alkaline developer to form a second resist pattern includes dissolving away the first resist pattern which has been converted to be soluble in the alkaline developer and achieving reversal transfer of the first resist pattern to the second resist pattern, thereby forming a pattern resulting from reversal transfer of the first resist pattern and the second resist pattern.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the invention, a second positive resist composition serving as the reversal film-forming composition is coated onto the first positive resist pattern. Even when a second resist film serving as the reversal film is formed by coating the second positive resist composition in solution form in a hydroxyl-containing solvent or a highly polar solvent such as an ester or ketone, the second resist composition serving as the reversal film-forming material can be buried in gaps in the first positive resist pattern without causing damage to the first positive resist pattern. In addition, the positive pattern made of the first positive resist composition can be dissolved away in an alkaline developer. Thus positive/negative reversal can be carried out at a high accuracy through simple steps.

Image reversal from a positive pattern to a negative pattern by this method ensures that using a first fine line pattern, a fine space pattern of the same size can be reversal-formed. In the case of a trench pattern, a line pattern having a capability to form a finer feature size is formed through exposure, and this is converted into a trench pattern by the image reversal technology described above, whereby an ultra-fine trench pattern can be formed.

This positive/negative reversal method may be advantageously utilized in the following case. An overdose of exposure permits a finer size pattern to be formed from a positive pattern. While it is technically very difficult to form isolated spaces (trench pattern) below the exposure threshold, an ultra-fine trench pattern can be formed by first forming positive pattern lines thinner than the ordinary exposure threshold using an overdose of exposure and then reversing the pattern according to the method of the invention.

In this way, double patterning is enabled by transferring fine lines of the first resist to the second resist through positive/negative reversal, thereby forming an ultra-fine space pattern and subjecting the second resist to resolution.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically illustrates in cross-sectional view the pattern forming process of the invention, state (A) that a processable substrate and a first resist film are disposed on a substrate.

FIG. 2 schematically illustrates in cross-sectional view the pattern forming process of the invention, state (B) that the first resist film is exposed and developed.

FIG. 3 schematically illustrates in cross-sectional view the pattern forming process of the invention, the developed state (B-1) that lines of thinner size are finished in the resist film by over-exposure.

FIG. 4 schematically illustrates in cross-sectional view the pattern forming process of the invention, state (C) that the resist pattern is deprotected and crosslinked under the action of acid and heat.

FIG. 5 schematically illustrates in cross-sectional view the pattern forming process of the invention, state (D) that a pattern reversal film is coated.

FIG. 6 schematically illustrates in cross-sectional view the pattern forming process of the invention, state (D-1) that the first resist pattern has an increased height and a coating of the second resist has a reduced thickness, so that the first resist pattern converted to be soluble in alkaline developer is exposed to an alkaline developer.

FIG. 7 schematically illustrates in cross-sectional view the pattern forming process of the invention, state (E) that the reversed first resist is removed with an alkaline developer without patterning the second resist serving as a film subject to reversal transfer.

FIG. 8 schematically illustrates in cross-sectional view the pattern forming process of the invention, state (F-1) that exposure is made such that spaces of the second resist are formed between features of the reversed first resist pattern.

FIG. 9 schematically illustrates in cross-sectional view the pattern forming process of the invention, the double pattern formed state (F-2) that the first resist pattern which has been converted to be soluble in alkaline developer and the second resist film which has been exposed so as to form a space pattern between features of the first resist pattern are removed with an alkaline developer.

FIG. 10 schematically illustrates in cross-sectional view the pattern forming process of the invention, state (F-3) that exposure of the first resist film is performed at a position spaced apart from the first resist pattern to be reversed into spaces.

FIG. 11 schematically illustrates in cross-sectional view the pattern forming process of the invention, the double pattern formed state (F-4) state that the first resist pattern which has been converted to be soluble in alkaline developer and an isolated line pattern at a position spaced apart from the first resist pattern to be reversed are formed.

FIG. 12 is a plan view illustrating the pattern forming process of the invention, state (G-1) that on five Y-direction lines of the first pattern which result from the resist pattern being deprotected and crosslinked under the action of acid and heat, a second resist film is coated and exposed to a second pattern in the form of a cutout pattern extending perpendicular to the first pattern.

FIG. 13 is a plan view illustrating the pattern forming process of the invention, state (G-2) that the first pattern is positive/negative reversed by development and spaces of the second pattern are resolved at the same time.

FIG. 14 is a plan view illustrating the pattern forming process of the invention, state (H-1) that on five Y-direction lines of the first pattern which result from the resist pattern being deprotected and crosslinked under the action of acid and heat, a second resist film is coated and exposed to a second pattern to leave five X-direction lines extending perpendicular to the first pattern.

FIG. 15 is a plan view illustrating the pattern forming process of the invention, state (H-2) that the first pattern is positive/negative reversed by development and lines of the second pattern are interrupted by reversal of the first pattern at the same time whereby a fine dot pattern is resolved.

FIG. 16 is a plan view illustrating the pattern forming process of the invention, state (I-1) showing double (double dipole) exposures of X and Y lines.

FIG. 17 is a plan view illustrating the pattern forming process of the invention, state (I-2) that a dot pattern is formed in the first resist film by development and the first resist pattern is deprotected and crosslinked under the action of acid and heat.

FIG. 18 is a plan view illustrating the pattern forming process of the invention, state (I-3) that a second resist is coated, exposed to a pattern of holes disposed between dots of the first resist, and developed so that a hole pattern is formed through positive/negative reversal of the first resist pattern and a hole pattern of the second resist pattern is formed at the same time.

FIG. 19 schematically illustrates a resist pattern obtained in Examples 43 and 44.

FIG. 20 schematically illustrates a resist pattern in Comparative Example 9.

FIG. 21 schematically illustrates a resist pattern in Example 45.

FIG. 22 schematically illustrates a resist pattern in Comparative Example 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. As used herein, the notation (C_(n)-C_(m)) means a group containing from n to m carbon atoms per group. The abbreviation “phr” refers to parts by weight per 100 parts by weight of resin. The terms “converted” and “reversed” are used interchangeably in the context that resist film is converted from an alkali-insoluble state to an alkali-soluble state, and the same applies to the term “reversal.”

There were several problems to be overcome in the course of development works. In the situation where a reversal film is formed on a once formed positive pattern, how to deposit a new coating without disrupting the underlying pattern is one of such problems. Our initial approach to this problem is to form a reversal film after a positive pattern is crosslinked and insolubilized in a solvent.

In the invention, a film subject to reversal transfer is a second resist film so that double patterns may be formed. The inventors have found that insolubilization of the first pattern in a solvent used in coating of the second resist composition for forming a reversal film is implemented by utilizing crosslinking of the first pattern. It is preferred that this crosslinking reaction is performed by the existing technique or in the existing equipment in the current semiconductor device fabrication system, especially based on lithography. For example, it is believed unfavorable to introduce a high-energy radiation irradiating step capable of photo-reaction to facilitate crosslinking reaction because of a negative impact on productivity. It is also believed unfavorable to build a special expensive processing unit such as a high-energy radiation irradiating unit in the system.

It is desired that crosslinking of the pattern of first resist film to acquire resistance to an organic solvent used in the second resist film serving as the reversal film be accomplished only by high-temperature baking. If possible only by high-temperature baking, the invention achieves outstanding practical effects because high-temperature hot plates are commonly used in the semiconductor device fabrication system.

It is also required that crosslinking of the pattern of first resist film to acquire resistance to an organic solvent used in the second resist film serving as the reversal film do not detract from a high solubility in an alkaline developer for the second resist film essential for removing the second resist pattern.

Making studies on the composition of a first chemically amplified positive resist material and the treating conditions thereof so as to induce thermal crosslinkage to impart resistance to an organic solvent used in the second resist film serving as the reversal film, the inventors have reached the present invention.

Another problem to be overcome is how to selectively remove the first positive pattern relative to the reversal film. Like the equipment referred to above, the means of removing the first pattern also exists in the current semiconductor fabrication system. In particular, it is preferred to remove the first pattern by the existing technique or unit used in the lithography system. It would be desirable to effect removal simply with an alkaline developer. Dry etching may also be used, with the disadvantages of process complexity and a lower throughput. It is desired to remove the first pattern by means of an alkaline development unit existing in the lithography system and transfer its image to a second pattern if possible.

It has been found that the pattern of unexposed areas in the first positive resist film is, of course, insoluble in an alkaline developer because alkali-soluble groups are kept protected with acid labile groups which are eliminatable with acid, and that when heated, a minor amount of acid which has diffused from exposed areas and remains in the pattern reacts with acid labile groups at high temperature to eliminate the acid labile groups so that the pattern of first positive resist film becomes alkali soluble. It has also been found that some acid labile groups are thermally eliminated by heating at high temperature. It is confirmed that by heating at high temperature, the first resist pattern is converted from the alkaline developer-insoluble positive behavior to an alkaline developer-soluble behavior. The reversal of the positive pattern of first resist film to alkaline solubility means that the first resist film can be readily removed together with the second resist film subject to reversal transfer, using an alkaline developer. The reversed first resist pattern can be removed more readily than the second resist film during the alkaline development step of patterning the second resist film, achieving a high efficiency.

Making studies on a first resist composition and treating conditions thereof so as to induce crosslinking reaction in the first resist pattern to enhance resistance to an organic solvent used in coating of a second resist film subject to reversal transfer while maintaining alkali solubility of the reversed first resist pattern, the inventors have established a double pattern forming process involving reversal transfer of the first positive resist film to the second resist film and patterning of the second resist film.

Besides the problems to be overcome, there are several issues which must be taken into account in the practice of the invention.

A first issue relates to the thickness of a first resist film and a second resist film. To remove the first resist pattern which has been converted to be alkali soluble from the second resist film during alkaline development, the top of the first resist pattern must be exposed over the upper surface of the second resist film because otherwise the first resist pattern is not contacted with the alkaline developer or removed. Accordingly, it must be considered that the height of the first resist film pattern is increased and the coating thickness of the second resist film is reduced. However, it is generally believed favorable that the second resist film overlies and covers the first resist pattern because otherwise the height (aspect ratio =height/size of line pattern) of the second resist pattern becomes lower and due to process management. Coverage of the first resist pattern with the second resist film ensures that the second resist film is buried close between features of the first resist pattern. Coverage of the first resist pattern with the second resist film, however, prevents the reversed first resist pattern from being removed by alkaline development. Thus the second resist film is designed to have some solubility in an alkaline developer so that the second resist film is somewhat slimmed (reduced in thickness) with the alkaline developer to provide access to alkali-soluble portions of the first resist pattern by the alkaline developer, allowing the developer to contact the first resist pattern.

As described just above, the second resist film to which the first resist pattern is reversal transferred is designed to have such a solubility in an alkaline developer that the alkaline developer may gain access to the first resist film.

However, it must be borne in mind that the film to which the first resist pattern is transferred is the second resist film to be patterned. The provision of the second resist film with a rate of dissolution in an alkaline developer may lead to degradation of the dissolution contrast of the second resist film that governs its resolution performance. This, in turn, leads to a likelihood of degrading the patterning performance of the second resist film and degrading process margins such as a decline of bridge margin. In particular, substantial slimming during patterning of the second resist film is not preferable because the resist pattern loss that the height of finished resist pattern is reduced becomes noticeable, and a degradation of profile resulting from pattern edge chipping is observed.

Continuing research works, the inventors have made the following discovery. Even when the first resist pattern is completely overlaid with the second resist film, the inventors have succeeded in removing the reversed first resist film from the second resist film by an alkaline developer, thereby transferring the reversed first resist pattern to the second resist film, without a need to provide the second resist film with a certain rate of dissolution in an alkaline developer so that the alkaline developer may gain access to the first resist film. More specifically, some acid which has diffused from exposed areas and remains in the first resist pattern or the acid generated by thermal decomposition of the photoacid generator in the resist composition remaining in the first resist pattern during the step of heating at high temperature for endowing the first resist pattern with resistance to solvent for the second resist film while maintaining a solubility in alkaline developer of the first resist pattern, acts on alkali-soluble groups protected with acid labile groups which are eliminatable with acid in the second resist film overlying the first resist pattern, whereby acid elimination occurs in the baking steps of a process involving coating, prebaking, exposure and post-exposure baking the second resist film. The second resist film overlying the first resist pattern is then converted to be alkali soluble. Then, during the development step for patterning the second resist film, the second resist film overlying the first resist pattern is dissolved away and the reversed first resist pattern is also removed.

As described above, it has been found that the reversed first resist pattern can be removed from the second resist film without a need to provide the second resist film with a certain rate of dissolution in alkaline developer. Of course, if the thickness of the second resist film coated is extremely thick, or if the second resist film overlying the first resist pattern is extremely thick, then the acid originating from the first resist pattern and migrating outward does not fully permeate into the second resist film containing acid labile groups which are eliminatable with acid, thus failing to convert the second resist film overlying the first resist pattern to be alkali soluble and restraining the alkaline developer from reaching the reversed first resist pattern. This leads to a failure in removal of the reversed first resist pattern and in reversal transfer of the first resist pattern to the second resist film. It is then absolutely essential that the thickness of the second resist film be thinner than the thickness of the first resist film, provided that the thickness is measured as coated on a flat substrate. In an example where the first resist film is coated to a thickness of 1,200 Å on a flat substrate, if the second resist film is coated to a thickness of 600 Å on a flat substrate, the second resist film is buried close between features of the first resist pattern and also overlies the first resist pattern. Since the second resist film overlying the first resist film is converted to be alkali soluble under the action of acid generated from the first resist pattern, the overlying second resist film and the reversed first resist pattern are simultaneously removed by an alkaline developer.

The height of the first resist pattern is also an important consideration. When the first resist film is coated and patterned, the resulting first resist pattern often suffers from a top loss, that is, becomes lower in height. In addition, the first resist pattern undergoes thermal shrinkage under the action of heat released in the step of heating at high temperature the first resist pattern to induce crosslinking reaction to enhance its resistance to solvent used in coating of the second resist film, and this thermal shrinkage must also be taken into account. Therefore, the height of the first resist pattern prior to coating of the second resist film is important. The second resist film must be buried in the first resist pattern beyond that height, and overlie the first resist pattern. In addition, the thickness of a portion of the second resist film overlying the first resist pattern should be such that the acid originating from the first resist film may permeate into the second resist film to induce acid-assisted elimination of acid labile groups therein.

It is preferred, needless to say, that the height of the first resist pattern prior to coating of the second resist film be higher, and the first resist pattern experience a less top loss. The reason is that if the first resist film experiences a substantial top loss and its pattern has a reduced height, the second resist film overlying the first resist pattern becomes thin and so, the double patterns including the reversal-transferred first resist pattern and the second resist pattern are finished to a reduced height (aspect ratio). The first resist composition must be formulated so that the first resist pattern subject to reversal transfer may have a height.

With the height of the first resist film as patterned taken into account, the preferred thicknesses of the first and second resist films coated are as follows. The thickness of the second resist film as coated on a flat substrate is preferably 60% to 50% of the thickness of the first resist film as coated on a flat substrate. If their thicknesses are below the range, the double patterns including the pattern of reversal transfer of the first resist film and the second resist pattern fail to acquire a height.

As described above, some acid which has diffused from exposed areas and remains in the first resist pattern or the acid generated by thermal decomposition of the photoacid generator in the resist composition remaining in the first resist pattern during the step of heating at high temperature for endowing the first resist pattern with resistance to solvent for the second resist film while maintaining a solubility in alkaline developer of the first resist pattern acts on alkali-soluble groups protected with acid labile groups which are eliminatable with acid in the second resist film overlying the first resist pattern, whereby acid elimination occurs in the baking steps of a process involving coating, prebaking, exposure and post-exposure baking the second resist film. The second resist film overlying the first resist pattern is then converted to be alkali soluble. Then, during the development step for patterning the second resist film, the second resist film overlying the first resist pattern is dissolved away and the reversed first resist pattern is also removed simultaneously. In connection with this finding, positive addition to the first resist composition of a thermal acid generator capable of generating acid under the action of heat was devised for the purpose of making up for some acid which has diffused from exposed areas and remains in the first resist pattern or the acid generated by thermal decomposition of the photoacid generator in the resist composition remaining in the first resist pattern during the step of heating at high temperature for endowing the first resist pattern with solvent resistance. Regrettably, it was found that excess thermal acid generator added to the first resist film can adversely affect the resolution performance and process margin of the first resist film when it is patterned. For example, the thermal acid generators are ammonium salts of acids. It is inferred that an anion exchange occurs between the ammonium salt and an onium salt used as the photoacid generator within the resist material, failing to achieve the desired resolution capability. For example, a resist material having a thermal acid generator added is observed as behaving to enhance the diffusion of acid acting on acid labile groups within the resist film. The enhanced acid diffusion exacerbates process margins of a resist pattern to be formed such as exposure latitude and mask error factor (MEF). In addition, when a thermal acid generator is positively added, it functions advantageously to assist the first resist film in developing alkali solubility and promoting crosslinking reaction to endow resistance to organic solvent used in coating of the second resist film. However, if excess acid is generated and remains in the first resist film, it noticeably acts on acid labile groups in the second resist film, giving rise to the problem that in transfer of the reversed first resist pattern, acid labile groups in the second resist film serving as a transfer film change to be alkali soluble so that the size of the transferred pattern is enlarged. Moreover, if excess acid is generated and remains in the first resist pattern and diffuses noticeably into the second resist film, then it may act on acid labile groups throughout the second resist film. Then the overall second resist film is converted to be alkali soluble, failing to transfer the first resist pattern. In addition to a failure to form a second resist pattern, the overall second resist film is removed. At worst no films may be left behind.

It was also found that the addition of a thermal acid generator can deteriorate the thermal properties of the first resist film. The thermal acid generator added behaves as a plasticizer in the step of heating at high temperature the first resist pattern to induce crosslinkage to endow it with resistance to solvent for the second resist film, giving rise to the problem that the first resist pattern undergoes thermal flow during this heating step.

As discussed above, the addition of a thermal acid generator to the first resist composition is preferred in that it assists the first resist film in developing alkaline solubility and promotes crosslinking reaction to endow resistance to organic solvent used in coating of the second resist film, but excess addition gives rise to several problems. The thermal acid generator is added in such amounts as to avoid any substantial impacts on the lithography of patterning the first resist film, on the thermal properties of the first resist film, and on the second resist film. The amount of thermal acid generator added is generally up to 5%, preferably up to 3%, and more preferably 1 to 0.01% based on the weight of the base resin in the first resist composition.

While several issues to be considered in the practice of the invention are discussed, attention must also be paid to the thermal properties of the first resist film and the temperature associated with the step of heating at high temperature the first resist film to assist the first resist film in developing alkaline solubility and to facilitate crosslinking reaction to endow it with resistance to organic solvent used in coating of the second resist film.

The temperature associated with the step of heating at high temperature the first resist film to assist the first resist film in developing alkaline solubility and to facilitate crosslinking reaction to endow it with resistance to organic solvent used in coating of the second resist film should desirably be higher than the temperatures encountered in the process for patterning the first resist film involving coating, prebaking, exposure and post-exposure baking. If crosslinking reaction occurs even at a temperature which is close to the temperatures of prebaking and post-exposure baking in the first resist film patterning process, this leads to the risk that crosslinking reaction takes place during patterning of the first resist film, failing to avoid negative impacts on lithographic characteristics. It is undesirable that crosslinking reaction occur at a higher temperature than the glass transition temperature (Tg) of the first resist pattern. The reason is that if the first resist pattern is heated at a higher temperature than its Tg, the first resist pattern undergoes thermal flow to enlarge the pattern size or to disable fine-size processing. If thermal flow occurs, the resist pattern is reduced in height, which is also undesirable.

The temperature associated with the step of heating at high temperature the first resist film to assist the first resist film in developing alkaline solubility and to facilitate crosslinking reaction to endow it with resistance to organic solvent used in coating of the second resist film is preferably at least 150° C., and more preferably in the range of 180 to 220° C. A photoacid generator and a basic compound in a resist material generally serve as plasticizers to reduce the Tg of the resist pattern so that the thermal flow incipient temperature becomes lower. Since the photoacid generator and basic compound are essential components in the resist material, the Tg of resist base resin itself must be elevated depending on the addition and plasticizing effects of these components. Accordingly, the resist base resin has an optimum Tg of at least 150° C., and preferably at least 180° C. If the heating temperature to facilitate crosslinking reaction is above 220° C., an appropriate first resist pattern to be reversal-transferred to the second resist film cannot be formed due to substantial thermal shrinkage and thermal damages of the first resist film. As discussed above, any crosslinking reaction hardly takes place when the heating temperature to facilitate crosslinking reaction is below 150° C.

A further issue to be considered in the practice of the invention is a rate of dissolution in alkaline developer of the first resist film which has been converted to be alkali soluble. As described above, a minor amount of acid which has diffused from exposed areas and remains in the pattern reacts with acid labile groups at high temperature to eliminate the acid labile groups so that the first positive resist pattern becomes alkali soluble, and some acid labile groups are thermally eliminated by heating at high temperature. Thus, the first resist pattern can be converted from the alkaline developer-insoluble positive behavior to the alkaline developer-soluble behavior by heating at high temperature. An appropriate measure of dissolution rate is that the reversed first resist pattern has a dissolution rate in excess of 2 nm/sec when developed with a 2.38 wt % aqueous solution of tetramethylammonium hydroxide (TMAH) commonly used in the alkaline development of resist films.

Making extensive investigations on the task of converting the first positive resist pattern to be alkali soluble, the task of endowing the first resist pattern with organic solvent resistance during coating of the second resist film serving as a reversal transfer film, and other issues to be overcome in implementing the invention, the inventors have completed the double patterning process.

Now the invention is described in further detail.

The base resin in the first positive resist composition used in the pattern forming process is advantageously a polymer comprising recurring units having a lactone ring, more specifically recurring units having a 7-oxanorbornane ring, and preferably recurring units of the general formula (a). These units are used as adhesive units. The process is advantageously applicable with this polymer without adding a further component(s) to the base resin.

Herein R¹ is hydrogen or methyl, R² is a single bond or a straight, branched or cyclic C₁-C₆ alkylene group which may have an ether (—O—) or ester (—COO—) group, and which has a primary or secondary carbon atom through which it is linked to the ester moiety in the formula, R³, R⁴, and R⁵ are each independently hydrogen or a straight, branched or cyclic C₁-C₆ alkyl group, and “a” is a number in the range: 0<a<1.0.

Examples of the C₁-C₆ alkylene group include methylene, ethylene, n-propylene, isopropylene, n-butylene, isobutylene, sec-butylene, n-pentylene, isopentylene, cyclopentylene, n-hexylene, and cyclohexylene.

Examples of the C₁-C₆ alkyl group include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, n-pentyl, isopentyl, cyclopentyl, n-hexyl, and cyclohexyl.

The monomers from which recurring units of formula (a) are derived are monomers Ma of the following formula wherein R¹ to R⁶ are as defined above.

Examples of monomers Ma are shown below.

In the embodiment of the process, once a first resist pattern is formed through exposure and development, deprotection of acid labile groups and crosslinking are brought about under the action of acid and heat. A second resist film serving as a reversal film is coated thereon, patterned and alkali developed. The first resist pattern is removed at the same time as the last development, forming double patterns.

The acid contributing to crosslinking reaction may include the acid which has diffused from exposed areas and remains in the first resist pattern and the acid resulting from thermal decomposition of the residual photoacid generator by heating. Further a minor amount of a thermal acid generator capable of generating an acid upon heating may be added to the resist composition.

The first resist pattern based on the polymer comprising recurring units having 7-oxanorbornane rings and recurring units having acid labile groups is converted into a film which is alkali soluble as a result of deprotection of acid labile groups and into a film which is insoluble in a solvent (i.e., solvent in a reversal film or second resist pattern-forming composition) as a result of crosslinking of 7-oxanorbornane ring. Therefore, even when a solution of reversal or second resist film-forming material in an organic solvent is coated on the first resist pattern, no intermixing occurs between the first resist pattern and the reversal film-forming second resist composition.

During subsequent treatment with an alkaline developer for patterning the second resist film, a surface layer of the reversal or second resist film is dissolved down to the level of the first resist pattern, after which dissolution of the first resist pattern is commenced, whereby image reversal is accomplished. With respect to the dissolution mechanism that the second resist film (subject to reversal transfer) overlying the first resist pattern is dissolved down to the level of the reversed first resist pattern, the second resist film subject to reversal transfer may be previously given a rate of alkaline dissolution. Alternatively, the acid present in the first resist pattern reacts with acid labile groups in the second resist film overlying the first resist pattern during the prebaking and post-exposure baking in the second resist patterning process whereby the acid labile groups are eliminated so that the second resist film is converted to be alkali soluble, allowing the alkaline developer to reach the reversed first resist pattern whereby the first resist pattern can be dissolved away in the alkaline developer and removed.

If a polymer comprising oxirane or oxetane-bearing recurring units is used as the resist base resin, it fails to function as the desired first positive resist material in the inventive process, because the oxirane or oxetane ring has so high a rate of acid-catalyzed cleavage reaction that crosslinking takes place at the resist processing temperature, for example, a post-exposure baking (PEB) temperature of about 90 to 130° C., whereby the polymer becomes alkali insoluble. In contrast, the inventive polymer undergoes no crosslinking at the heating temperature range of PEB because the 1,4-epoxy bond of 7-oxanorbornane ring is low reactive in the acid-catalyzed cleavage reaction as compared with the oxirane or oxetane ring. The recurring units having 7-oxanorbornane ring are stable relative to acid during the process until development, and serve as hydrophilic groups to exert the function of improving adhesion and alkali solubility. However, under the action of acid remaining in the pattern after development or acid generated upon heating and heating at or above 160° C., the 1,4-epoxy bond of 7-oxanorbornane ring is cleaved so that crosslinking reaction takes place whereby the polymer becomes insoluble in the solvent and at the same time, the acid and heat cause deprotection of acid labile groups whereby alkali solubility is increased.

The base resin in the first positive resist composition used in the pattern forming process is advantageously a polymer comprising crosslinkable recurring units represented by the general formula (a) and recurring units having an acid labile group represented by the following general formula (b).

Herein R⁶ is hydrogen or methyl, R⁷ is an acid labile group, and b is a number in the range: 0<b≦0.8.

The monomers from which recurring units of formula (b) are derived are monomers Mb of the following general formula wherein R⁶ and R⁷ are as defined above.

The acid labile group represented by R⁷ in formula (b) may be selected from a variety of such groups, specifically groups of the following formulae (AL-10) and (AL-11), tertiary alkyl groups of the following formula (AL-12), and oxoalkyl groups of 4 to 20 carbon atoms, but not limited thereto.

In formulae (AL-10) and (AL-11), R⁵¹ and R⁵⁴ each are a monovalent hydrocarbon group, typically a straight, branched or cyclic alkyl group of 1 to 40 carbon atoms, more specifically 1 to 20 carbon atoms, which may contain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. The subscript “a5” is an integer of 0 to 10, and especially 1 to 5. R⁵² and R⁵³ each are hydrogen or a monovalent hydrocarbon group, typically a straight, branched or cyclic C₁-C₂₀ alkyl group, which may contain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. Alternatively, a pair of R⁵² and R⁵³, R⁵² and R⁵⁴, or R⁵³ and R⁵⁴, taken together, may form a ring, specifically aliphatic ring, with the carbon atom or the carbon and oxygen atoms to which they are attached, the ring having 3 to 20 carbon atoms, especially 4 to 16 carbon atoms.

In formula (AL-12), R⁵⁵, R⁵⁶ and R⁵⁷ each are a monovalent hydrocarbon group, typically a straight, branched or cyclic C₁-C₂₀ alkyl group, which may contain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. Alternatively, a pair of R⁵⁵ and R⁵⁶, R⁵⁵ and R⁵⁷, or R⁵⁶ and R⁵⁷, taken together, may form a ring, specifically aliphatic ring, with the carbon atom to which they are attached, the ring having 3 to 20 carbon atoms, especially 4 to 16 carbon atoms.

Illustrative examples of the groups of formula (AL-10) include tert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amyloxycarbonyl, tert-amyloxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl, 2-tetrahydropyranyloxycarbonylmethyl and 2-tetrahydrofuranyloxycarbonylmethyl as well as substituent groups of the following formulae (AL-10)-1 to (AL-10)-10.

In formulae (AL-10)-1 to (AL-10)-10, R⁵ is independently a straight, branched or cyclic C₁-C₈ alkyl group, C₆-C₂₀ aryl group or C₇-C₂₀ aralkyl group; R⁵⁹ is hydrogen or a straight, branched or cyclic C₁-C₂₀ alkyl group; R⁶⁰ is a C₆-C₂₀ aryl group or C₇-C₂₀ aralkyl group; and “a5” is an integer of 0 to 10.

Illustrative examples of the acetal group of formula (AL-11) include those of the following formulae (AL-11)-1 to (AL-11)-34.

Other examples of acid labile groups include those of the following formula (AL-11a) or (AL-11b) while the polymer may be crosslinked within the molecule or between molecules with these acid labile groups.

Herein R⁶¹ and R⁶² each are hydrogen or a straight, branched or cyclic C₁-C₈ alkyl group, or R⁶¹ and R⁶², taken together, may form a ring with the carbon atom to which they are attached, and R⁶¹ and R⁶² are straight or branched C₁-C₈ alkylene groups when they form a ring. R⁶³ is a straight, branched or cyclic C₁-C₁₀ alkylene group. Each of b5 and d5 is 0 or an integer of 1 to 10, preferably 0 or an integer of 1 to 5, and c5 is an integer of 1 to 7. “A” is a (c5+1)-valent aliphatic or alicyclic saturated hydrocarbon group, aromatic hydrocarbon group or heterocyclic group having 1 to 50 carbon atoms, which may be separated by a heteroatom such as oxygen, sulfur or nitrogen or in which some of the hydrogen atoms attached to carbon atoms may be substituted by hydroxyl, carboxyl, carbonyl groups or fluorine atoms. “B” is —CO—O—, —NHCO—O— or —NHCONH—.

Preferably, “A” is selected from divalent to tetravalent, straight, branched or cyclic C₁-C₂₀ alkylene, alkanetriyl and alkanetetrayl groups, and C₆-C₃₀ arylene groups, which may be separated by a heteroatom such as oxygen, sulfur or nitrogen or in which some of the hydrogen atoms attached to carbon atoms may be substituted by hydroxyl, carboxyl, acyl groups or halogen atoms. The subscript c5 is preferably an integer of 1 to 3.

The crosslinking acetal groups of formulae (AL-11a) and (AL-11b) are exemplified by the following formulae through (AL-11)-42.

Illustrative examples of the tertiary alkyl of formula (AL-12) include tert-butyl, triethylcarbyl, 1-ethylnorbornyl, 1-methylcyclohexyl, 1-ethylcyclopentyl, and tert-amyl groups as well as those of (AL-12)-1 to (AL-12)-16.

Herein R⁶⁴ is independently a straight, branched or cyclic C₁-C₈ alkyl group, C₆-C₂₀ aryl group or C₇-C₂₀ aralkyl group; R⁶⁵ and R⁶⁷ each are hydrogen or a straight, branched or cyclic C₁-C₂₀ alkyl group; and R⁶⁶ is a C₆-C₂₀ aryl group or C₇-C₂₀ aralkyl group.

With R⁶⁸ representative of a di- or more valent alkylene or arylene group included as shown in formulae (AL-12)-17 and (AL-12)-18, the polymer may be crosslinked within the molecule or between molecules. In formulae (AL-12)-17 and (AL-12)-18, R⁶⁴ is as defined above; R⁶⁸ is a straight, branched or cyclic C₁-C₂₀ alkylene group or arylene group, which may contain a heteroatom such as oxygen, sulfur or nitrogen; and b6 is an integer of 1 to 3.

The groups represented by R⁶⁴, R⁶⁵, R⁶⁶ and R⁶⁷ may contain a heteroatom such as oxygen, nitrogen or sulfur. Such groups are exemplified by those of the following formulae (AL-13)-1 to (AL-13)-7.

Of the acid labile groups of formula (AL-12), recurring units having an exo-form structure represented by the formula (AL-12)-19 are preferred.

Herein, R⁶⁹ is a straight, branched or cyclic C₁-C₈ alkyl group or a substituted or unsubstituted C₆-C₂₀ aryl group; R⁷⁰ to R⁷⁵, R⁷⁸ and R⁷⁹ are each independently hydrogen or a monovalent hydrocarbon group, typically alkyl, of 1 to 15 carbon atoms which may contain a heteroatom; and R⁷⁶ and R⁷⁷ are hydrogen. Alternatively, a pair of R⁷⁰ and R⁷¹, R⁷² and R⁷⁴, R⁷² and R⁷⁵, R⁷³ and R⁷⁵, R⁷³ and R⁷⁹, R⁷⁴ and R⁷⁸, R⁷⁶ and R⁷⁷, or R⁷⁸, taken together, may form a ring, specifically aliphatic ring, with the carbon atom(s) to which they are attached, and in this case, each R is a divalent hydrocarbon group, typically alkylene, of 1 to 15 carbon atoms which may contain a heteroatom. Also, a pair of R⁷⁰ and R⁷⁹, R⁷⁶ and R⁷⁹, or R⁷² and R⁷⁴ which are attached to vicinal carbon atoms may bond together directly to form a double bond. The formula also represents an enantiomer.

The ester form monomers from which recurring units having an exo-form structure represented by the formula (AL-12)-19:

are derived are described in U.S. Pat. No. 6,448,420 (JP-A 2000-327633). It is noted that R and R are each independently hydrogen, methyl, —COOCH₃, —CH₂COOCH₃ or the like. Illustrative non-limiting examples of suitable monomers are given below.

Also included in the acid labile groups of formula (AL-12) are acid labile groups having furandiyl, tetrahydrofurandiyl or oxanorbornanediyl as represented by the following formula (AL-12)-20.

Herein, R⁸⁰ and R⁸¹ are each independently a monovalent hydrocarbon group, typically a straight, branched or cyclic C₁-C₁₀ alkyl. R⁸⁰ and R⁸¹, taken together, may form an aliphatic hydrocarbon ring of 3 to 20 carbon atoms with the carbon atom to which they are attached. R⁸² is a divalent group selected from furandiyl, tetrahydrofurandiyl and oxanorbornanediyl. R⁸³ is hydrogen or a monovalent hydrocarbon group, typically a straight, branched or cyclic C₁-C₁₀ alkyl, which may contain a heteroatom.

Examples of the monomers from which the recurring units substituted with acid labile groups having furandiyl, tetrahydrofurandiyl and oxanorbornanediyl as represented by the formula:

(wherein R⁸⁰ to R⁸³, and R¹¹² are as defined above) are derived are shown below. Note that Me is methyl and Ac is acetyl.

While the polymer used herein preferably includes recurring units of formula (a) and recurring units of formula (b), it may have copolymerized therein recurring units (d) derived from monomers having adhesive groups such as hydroxy, cyano, carbonyl, ester, ether groups, lactone rings, carbonyl groups or carboxylic anhydride groups. Examples of monomers from which recurring units (d) are derived are given below.

Of the recurring units (d), those having an α-trifluoromethyl alcohol group or carboxyl group are preferably incorporated in copolymers because they improve the alkali dissolution rate of the developed pattern after heating. Examples of recurring units having a carboxyl group are given below.

In the polymer of the invention, the recurring units (a), (b) and (d) are present in proportions a, b, and d, respectively, which satisfy the range: 0<a<1.0, 0<b≦0.8, 0.1≦a+b≦1.0, 0≦d<1.0, and preferably the range: 0.1≦a≦0.9, 0.1≦b≦0.7, 0.2≦a+b≦1.0, and 0≦d≦0.9, provided that a+b+d=1.

It is noted that the meaning of a+b=1 is that in a polymer comprising recurring units (a) and (b), the sum of recurring units (a) and (b) is 100 mol % based on the total amount of entire recurring units. The meaning of a+b<1 is that the sum of recurring units (a) and (b) is less than 100 mol % based on the total amount of entire recurring units, indicating the inclusion of other recurring units, for example, units (d).

The polymer serving as the base resin in the resist material used in the pattern forming process of the invention should preferably have a weight average molecular weight (Mw) in the range of 1,000 to 500,000, and more preferably 2,000 to 30,000, as measured by gel permeation chromatography (GPC) using polystyrene standards. With too low a Mw, the efficiency of thermal crosslinking in the resist material after development may become low. With too high a Mw, the polymer may lose alkali solubility and give rise to a footing phenomenon after pattern formation.

If a polymer has a wide molecular weight distribution or dispersity (Mw/Mn), which indicates the presence of lower and higher molecular weight polymer fractions, there is a possibility that foreign matter is left on the pattern or the pattern profile is degraded. The influences of molecular weight and dispersity become stronger as the pattern rule becomes finer. Therefore, the multi-component copolymer should preferably have a narrow dispersity (Mw/Mn) of 1.0 to 2.0, especially 1.0 to 1.5, in order to provide a resist composition suitable for micropatterning to a small feature size.

It is understood that a blend of two or more polymers which differ in compositional ratio, molecular weight or dispersity is acceptable.

The polymer as used herein may be synthesized by any desired method, for example, by dissolving unsaturated bond-containing monomers corresponding to the respective units (a), (b) and (d) in an organic solvent, adding a radical initiator thereto, and effecting heat polymerization. Examples of the organic solvent which can be used for polymerization include toluene, benzene, tetrahydrofuran, diethyl ether and dioxane. Examples of the polymerization initiator used herein include 2,2′-azobisisobutyronitrile (AIBN), 2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl 2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide. Preferably the system is heated at 50 to 80° C. for polymerization to take place. The reaction time is 2 to 100 hours, preferably 5 to 20 hours. The acid labile group that has been incorporated in the monomers may be kept as such, or the acid labile group may be once removed with an acid catalyst and thereafter protected or partially protected.

As described previously, the pattern forming process of the invention comprises the steps of coating the positive resist composition described above onto a substrate, prebaking the resist composition to form a resist film, exposing a selected area of the resist film to high-energy radiation, post-exposure baking, and developing the resist film with an alkaline developer to dissolve the exposed area thereof to form a resist pattern such as a line pattern. The subsequent step is to treat the resist pattern (area unexposed to high-energy radiation) so as to utilize the acid remaining in the resist pattern or to generate acid, thereby eliminating acid labile groups on the polymer (i.e., deprotection) and inducing crosslinking in the polymer. In this deprotected and crosslinked state, the polymer has a dissolution rate in excess of 2 nm/sec, preferably of 3 to 5,000 nm/sec, and more preferably 4 to 4,000 nm/sec in an alkaline developer. It is preferred in attaining the objects of the invention that the dissolution rate of the polymer is higher than the dissolution rate of the second resist material to form a reversal film in the same alkaline developer by a factor of 2 to 250,000, and especially 5 to 10,000.

In order that the polymer have a desired dissolution rate in the deprotected and crosslinked state, the polymer formulation is preferably designed such that the acid labile group-bearing recurring units of formula (b) account for 10 mol % to 90 mol %, and more preferably 12 mol % to 80 mol % of the entire recurring units.

First Resist Composition

The resist composition, specifically chemically amplified positive resist composition, used in the pattern forming process of the invention may further comprise an organic solvent, a compound capable of generating an acid in response to high-energy radiation (known as “acid generator”), and optionally, a dissolution inhibitor, a basic compound, a surfactant, and other components.

Solvent

The organic solvent used herein may be any organic solvent in which the base resin, acid generator, and other components are soluble. Illustrative, non-limiting, examples of the organic solvent include ketones such as cyclohexanone and methyl-2-n-amylketone; alcohols such as 3-methoxybutanol, 3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, and 1-ethoxy-2-propanol; ethers such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, propylene glycol monoethyl ether, ethylene glycol monoethyl ether, propylene glycol dimethyl ether, and diethylene glycol dimethyl ether; esters such as propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butyl acetate, tert-butyl propionate, and propylene glycol mono-tert-butyl ether acetate; and lactones such as γ-butyrolactone. These solvents may be used alone or in combinations of two or more thereof. Of the above organic solvents, diethylene glycol dimethyl ether, 1-ethoxy-2-propanol and propylene glycol monomethyl ether acetate, and mixtures thereof are preferred because the acid generator is most soluble therein.

The organic solvent is preferably used in an amount of about 200 to 3,000 parts by weight, more preferably about 400 to 2,000 parts by weight per 100 parts by weight of the base resin.

Acid Generator

The acid generators used herein include the following:

-   (i) onium salts of the formula (P1a-1), (P1a-2), (P1a-3) or (P1b), -   (ii) diazomethane derivatives of the formula (P2), -   (iii) glyoxime derivatives of the formula (P3), -   (iv) bissulfone derivatives of the formula (P4), -   (v) sulfonic acid esters of N-hydroxyimide compounds of the formula     (P5), -   (vi) β-ketosulfonic acid derivatives, -   (vii) disulfone derivatives, -   (viii) nitrobenzylsulfonate derivatives, and -   (ix) sulfonate derivatives.

These acid generators are described in detail.

(i) Onium Salts of Formula (P1a-1), (P1a-2) and (P1a-3):

Herein, R^(101a), R^(101b), and R^(101c) independently represent straight, branched or cyclic alkyl, alkenyl, oxoalkyl or oxoalkenyl groups of 1 to 12 carbon atoms, aryl groups of 6 to 20 carbon atoms, or aralkyl or aryloxoalkyl groups of 7 to 12 carbon atoms, wherein some or all of the hydrogen atoms may be replaced by alkoxy groups. Also, R^(101b) and R^(101c), taken together, may form a ring with the sulfur or iodine atom to which they are attached. R^(101b) and R^(101c) each are alkylene groups of 1 to 6 carbon atoms when they form a ring. K⁻ is a sulfonate in which at least one alpha-position is fluorinated, or a perfluoroalkylimidate or perfluoroalkylmethidate. R^(101d), R^(101e), R^(101f), and R^(101g) stand for hydrogen atoms, straight, branched or cyclic alkyl, alkenyl, oxoalkyl or oxoalkenyl groups of 1 to 12 carbon atoms, aryl groups of 6 to 20 carbon atoms, or aralkyl or aryloxoalkyl groups of 7 to 12 carbon atoms, wherein some or all of the hydrogen atoms may be replaced by alkoxy groups. A pair of R^(101d) and R^(101e) or a combination of R^(101d), R^(101e) and R^(101f) may form a ring with the nitrogen atom to which they are attached, and each of R^(101d) and R^(101e) or each of R^(101d), R^(101e) and R^(101f) is an alkylene group of 3 to 10 carbon atoms or a hetero-aromatic ring having the nitrogen atom (in the formula) incorporated therein, when they form a ring.

Of the onium salts having formulae (P1a-1), (P1a-2) and (P1a-3), those of formula (P1a-1) function as a photoacid generator, those of formula (P1a-2) function as a thermal acid generator, and those of formula (P1a-3) have both the functions of a photoacid generator and a thermal acid generator. In a system having (P1a-1) combined with (P1a-2), generator (P1-a) generates an acid upon exposure, with which pattern formation is performed, and generator (P1a-2) generates an acid when heated at high temperature after development, with which crosslinking is efficiently performed.

Examples of K include perfluoroalkanesulfonates such as triflate and nonaflate; imidates such as bis(trifluoromethylsulfonyl)imide, bis(perfluoroethylsulfonyl)imide, and bis(perfluorobutylsulfonyl)imide; methidates such as tris(trifluoromethylsulfonyl)methide and tris(perfluoroethylsulfonyl)methide; sulfonates having fluorine substituted at α-position as represented by of the general formula (K-1) and sulfonates having fluorine substituted at α-position as represented by of the general formula (K-2).

In formula (K-1), R^(102a) is a hydrogen atom, or a straight, branched or cyclic C₁-C₂₀ alkyl or acyl group, C₂-C₂₀ alkenyl group, or C₆ - C₂₀ aryl or aryloxy group, which may have an ether group, ester group, carbonyl group or lactone ring, or in which some or all hydrogen atoms may be substituted by fluorine atoms. In formula (K-2), R^(102b) is a hydrogen atom, or a straight, branched or cyclic C₁-C₂₀ alkyl group, C₂-C₂₀ alkenyl group, or C₆-C₂₀ aryl group.

R^(101a), R^(101b), and R^(101c) may be the same or different and are illustrated below. Exemplary alkyl groups include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclopropylmethyl, 4-methylcyclohexyl, cyclohexylmethyl, norbornyl, and adamantyl. Exemplary alkenyl groups include vinyl, allyl, propenyl, butenyl, hexenyl, and cyclohexenyl. Exemplary oxoalkyl groups include 2-oxocyclopentyl and 2-oxocyclohexyl as well as 2-oxopropyl, 2-cyclopentyl-2-oxoethyl, 2-cyclohexyl-2-oxoethyl, and 2-(4-methylcyclohexyl)-2-oxoethyl. Exemplary oxoalkenyl groups include 2-oxo-4-cyclohexenyl and 2-oxo-4-propenyl. Exemplary aryl groups include phenyl and naphthyl; alkoxyphenyl groups such as p-methoxyphenyl, m-methoxyphenyl, o-methoxyphenyl, ethoxyphenyl, p-tert-butoxyphenyl, and m-tert-butoxyphenyl; alkylphenyl groups such as 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, ethylphenyl, 4-tert-butylphenyl, 4-butylphenyl, and dimethylphenyl; alkylnaphthyl groups such as methylnaphthyl and ethylnaphthyl; alkoxynaphthyl groups such as methoxynaphthyl and ethoxynaphthyl; dialkylnaphthyl groups such as dimethylnaphthyl and diethylnaphthyl; and dialkoxynaphthyl groups such as dimethoxynaphthyl and diethoxynaphthyl. Exemplary aralkyl groups include benzyl, phenylethyl, and phenethyl. Exemplary aryloxoalkyl groups are 2-aryl-2-oxoethyl groups such as 2-phenyl-2-oxoethyl, 2-(1-naphthyl)-2-oxoethyl, and 2-(2-naphthyl)-2-oxoethyl.

Examples of the non-nucleophilic counter ion represented by K⁻ include halide ions such as chloride and bromide ions; fluoroalkylsulfonate ions such as triflate, 1,1,1-trifluoroethanesulfonate, and nonafluorobutanesulfonate; arylsulfonate ions such as tosylate, benzenesulfonate, 4-fluorobenzenesulfonate, 1,2,3,4,5-pentafluorobenzenesulfonate; and alkylsulfonate ions such as mesylate and butanesulfonate.

Herein, R^(102a) and R^(102b) independently represent straight, branched or cyclic alkyl groups of 1 to 8 carbon atoms. R¹⁰³ represents a straight, branched or cyclic alkylene group of 1 to 10 carbon atoms. R^(104a) and R^(104b) independently represent 2-oxoalkyl groups of 3 to 7 carbon atoms. K⁻ is a non-nucleophilic counter ion.

Illustrative of the groups represented by R^(102a) and R^(102b) are methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, cyclopentyl, cyclohexyl, cyclopropylmethyl, 4-methylcyclohexyl, and cyclohexylmethyl. Illustrative of the groups represented by R¹⁰³ are methylene, ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, 1,4-cyclohexylene, 1,2-cyclohexylene, 1,3-cyclopentylene, 1,4-cyclooctylene, and 1,4-cyclohexanedimethylene. Illustrative of the groups represented by R^(104a) and R^(104b) are 2-oxopropyl, 2-oxocyclopentyl, 2-oxocyclohexyl, and 2-oxocycloheptyl. Illustrative examples of the counter ion represented by K are the same as exemplified for formulae (P1a-1) and (P1a-2).

(ii) Diazomethane Derivatives of Formula (P2)

Herein, R¹⁰⁵ and R¹⁰⁶ independently represent straight, branched or cyclic alkyl or halogenated alkyl groups of 1 to 12 carbon atoms, aryl or halogenated aryl groups of 6 to 20 carbon atoms, or aralkyl groups of 7 to 12 carbon atoms.

Of the groups represented by R¹⁰⁵ and R¹⁰⁶, exemplary alkyl groups include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, amyl, cyclopentyl, cyclohexyl, cycloheptyl, norbornyl, and adamantyl. Exemplary halogenated alkyl groups include trifluoromethyl, 1,1,1-trifluoroethyl, 1,1,1-trichloroethyl, and nonafluorobutyl. Exemplary aryl groups include phenyl; alkoxyphenyl groups such as p-methoxyphenyl, m-methoxyphenyl, o-methoxyphenyl, ethoxyphenyl, p-tert-butoxyphenyl, and m-tert-butoxyphenyl; and alkylphenyl groups such as 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, ethylphenyl, 4-tert-butylphenyl, 4-butylphenyl, and dimethylphenyl. Exemplary halogenated aryl groups include fluorophenyl, chlorophenyl, and 1,2,3,4,5-pentafluorophenyl. Exemplary aralkyl groups include benzyl and phenethyl.

(iii) Glyoxime Derivatives of Formula (P3)

Herein, R¹⁰⁷ R¹⁰⁸ and R¹⁰⁹ independently represent straight, branched or cyclic alkyl or halogenated alkyl groups of 1 to 12 carbon atoms, aryl or halogenated aryl groups of 6 to 20 carbon atoms, or aralkyl groups of 7 to 12 carbon atoms. Also, R¹⁰⁸ and R¹⁰⁹, taken together, may form a cyclic structure. R¹⁰⁸ and R¹⁰⁹ each are a straight or branched alkylene group of 1 to 6 carbon atoms when they form a cyclic structure. R¹⁰⁵ is as defined in formula (P2).

Illustrative examples of the alkyl, halogenated alkyl, aryl, halogenated aryl, and aralkyl groups represented by R¹⁰⁷, R¹⁰⁸, and R¹⁰⁹ are the same as exemplified for R¹⁰⁵ and R¹⁰⁶. Examples of the alkylene groups represented by R¹⁰⁸ and R¹⁰⁹ include methylene, ethylene, propylene, butylene, and hexylene.

(iv) Bissulfone Derivatives of Formula (P4)

Herein, R^(101a) and R^(101b) are as defined above.

(v) Sulfonic Acid Esters of N-Hydroxyimide Compounds of Formula (P5)

Herein, R¹¹⁰ is an arylene group of 6 to 10 carbon atoms, alkylene group of 1 to 6 carbon atoms, or alkenylene group of 2 to 6 carbon atoms wherein some or all of the hydrogen atoms may be replaced by straight or branched alkyl or alkoxy groups of 1 to 4 carbon atoms, nitro, acetyl, or phenyl groups. R¹¹¹ is a straight, branched or cyclic alkyl group of 1 to 8 carbon atoms, alkenyl, alkoxyalkyl, phenyl or naphthyl group wherein some or all of the hydrogen atoms may be replaced by alkyl or alkoxy groups of 1 to 4 carbon atoms, phenyl groups (which may have substituted thereon an alkyl or alkoxy of 1 to 4 carbon atoms, nitro, or acetyl group), hetero-aromatic groups of 3 to 5 carbon atoms, or chlorine or fluorine atoms.

Of the groups represented by R¹¹⁰, exemplary arylene groups include 1,2-phenylene and 1,8-naphthylene; exemplary alkylene groups include methylene, ethylene, trimethylene, tetramethylene, phenylethylene, and norbornane-2,3-diyl; and exemplary alkenylene groups include 1,2-vinylene, 1-phenyl-1,2-vinylene, and 5-norbornene-2,3-diyl. Of the groups represented by R¹¹¹, exemplary alkyl groups are as exemplified for R^(101a) to R^(101c); exemplary alkenyl groups include vinyl, 1-propenyl, allyl, 1-butenyl, 3-butenyl, isoprenyl, 1-pentenyl, 3-pentenyl, 4-pentenyl, dimethylallyl, 1-hexenyl, 3-hexenyl, 5-hexenyl, 1-heptenyl, 3-heptenyl, 6-heptenyl, and 7-octenyl; and exemplary alkoxyalkyl groups include methoxymethyl, ethoxymethyl, propoxymethyl, butoxymethyl, pentyloxymethyl, hexyloxymethyl, heptyloxymethyl, methoxyethyl, ethoxyethyl, propoxyethyl, butoxyethyl, pentyloxyethyl, hexyloxyethyl, methoxypropyl, ethoxypropyl, propoxypropyl, butoxypropyl, methoxybutyl, ethoxybutyl, propoxybutyl, methoxypentyl, ethoxypentyl, methoxyhexyl, and methoxyheptyl.

Of the substituents on these groups, the alkyl groups of 1 to 4 carbon atoms include methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl and tert-butyl; and the alkoxy groups of 1 to 4 carbon atoms include methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, isobutoxy, and tert-butoxy. The phenyl groups which may have substituted thereon an alkyl or alkoxy of 1 to 4 carbon atoms, nitro, or acetyl group include phenyl, tolyl, p-tert-butoxyphenyl, p-acetylphenyl and p-nitrophenyl. The hetero-aromatic groups of 3 to 5 carbon atoms include pyridyl and furyl.

Illustrative examples of the acid generator include:

onium salts such as diphenyliodonium trifluoromethanesulfonate, (p-tert-butoxyphenyl)phenyliodonium trifluoromethanesulfonate, diphenyliodonium p-toluenesulfonate, (p-tert-butoxyphenyl)phenyliodonium p-toluenesulfonate, triphenylsulfonium trifluoromethanesulfonate, (p-tert-butoxyphenyl)diphenylsulfonium trifluoromethanesulfonate, bis(p-tert-butoxyphenyl)phenylsulfonium trifluoromethanesulfonate, tris(p-tert-butoxyphenyl)sulfonium trifluoromethanesulfonate, triphenylsulfonium p-toluenesulfonate, (p-tert-butoxyphenyl)diphenylsulfonium p-toluenesulfonate, bis(p-tert-butoxyphenyl)phenylsulfonium p-toluenesulfonate, tris(p-tert-butoxyphenyl)sulfonium p-toluenesulfonate, triphenylsulfonium nonafluorobutanesulfonate, triphenylsulfonium butanesulfonate, trimethylsulfonium trifluoromethanesulfonate, trimethylsulfonium p-toluenesulfonate, cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate, cyclohexylmethyl(2-oxocyclohexyl)sulfonium p-toluenesulfonate, dimethylphenylsulfonium trifluoromethanesulfonate, dimethylphenylsulfonium p-toluenesulfonate, dicyclohexylphenylsulfonium trifluoromethanesulfonate, dicyclohexylphenylsulfonium p-toluenesulfonate, trinaphthylsulfonium trifluoromethanesulfonate, (2-norbornyl)methyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate, ethylenebis[methyl(2-oxocyclopentyl)sulfonium trifluoromethanesulfonate], and 1,2′-naphthylcarbonylmethyltetrahydrothiophenium triflate;

diazomethane derivatives such as bis(benzenesulfonyl)diazomethane, bis(p-toluenesulfonyl)diazomethane, bis(xylenesulfonyl)diazomethane, bis(cyclohexylsulfonyl)diazomethane, bis(cyclopentylsulfonyl)diazomethane, bis(n-butylsulfonyl)diazomethane, bis(isobutylsulfonyl)diazomethane, bis(sec-butylsulfonyl)diazomethane, bis(n-propylsulfonyl)diazomethane, bis(isopropylsulfonyl)diazomethane, bis(tert-butylsulfonyl)diazomethane, bis(n-amylsulfonyl)diazomethane, bis(isoamylsulfonyl)diazomethane, bis(sec-amylsulfonyl)diazomethane, bis(tert-amylsulfonyl)diazomethane, 1-cyclohexylsulfonyl-1-(tert-butylsulfonyl)diazomethane, 1-cyclohexylsulfonyl-1-(tert-amylsulfonyl)diazomethane, and 1-tert-amylsulfonyl-1-(tert-butylsulfonyl)diazomethane;

glyoxime derivatives such as bis-O-(p-toluenesulfonyl)-α-dimethylglyoxime, bis-O-(p-toluenesulfonyl)-α-diphenylglyoxime, bis-O-(p-toluenesulfonyl)-α-dicyclohexylglyoxime, bis-O-(p-toluenesulfonyl)-2,3-pentanedioneglyoxime, bis-O-(p-toluenesulfonyl)-2-methyl-3,4-pentanedioneglyoxime, bis-O-(n-butanesulfonyl)-α-dimethylglyoxime, bis-O-(n-butanesulfonyl)-α-diphenylglyoxime, bis-O-(n-butanesulfonyl)-α-dicyclohexylglyoxime, bis-O-(n-butanesulfonyl)-2,3-pentanedioneglyoxime, bis-O-(n-butanesulfonyl)-2-methyl-3,4-pentanedioneglyoxime, bis-O-(methanesulfonyl)-α-dimethylglyoxime, bis-O-(trifluoromethanesulfonyl)-α-dimethylglyoxime, bis-O-(1,1,1-trifluoroethanesulfonyl)-α-dimethylglyoxime, bis-O-(tert-butanesulfonyl)-α-dimethylglyoxime, bis-O-(perfluorooctanesulfonyl)-α-dimethylglyoxime, bis-O-(cyclohexanesulfonyl)-α-dimethylglyoxime, bis-O-(benzenesulfonyl)-α-dimethylglyoxime, bis-O-(p-fluorobenzenesulfonyl)-α-dimethylglyoxime, bis-O-(p-tert-butylbenzenesulfonyl)-α-dimethylglyoxime, bis-O-(xylenesulfonyl)-α-dimethylglyoxime, and bis-O-(camphorsulfonyl)-α-dimethylglyoxime;

bissulfone derivatives such as bisnaphthylsulfonylmethane, bistrifluoromethylsulfonylmethane, bismethylsulfonylmethane, bisethylsulfonylmethane, bispropylsulfonylmethane, bisisopropylsulfonylmethane, bis-p-toluenesulfonylmethane, and bisbenzenesulfonylmethane;

β-ketosulfone derivatives such as 2-cyclohexylcarbonyl-2-(p-toluenesulfonyl)propane and 2-isopropylcarbonyl-2-(p-toluenesulfonyl)propane;

disulfone derivatives such as diphenyl disulfone deratives and dicyclohexyl disulfone derivatives;

nitrobenzyl sulfonate derivatives such as 2,6-dinitrobenzyl p-toluenesulfonate and 2,4-dinitrobenzyl p-toluenesulfonate;

sulfonic acid ester derivatives such as 1,2,3-tris(methanesulfonyloxy)benzene, 1,2,3-tris(trifluoromethanesulfonyloxy)benzene, and 1,2,3-tris(p-toluenesulfonyloxy)benzene; and

sulfonic acid esters of N-hydroxyimides such as N-hydroxysuccinimide methanesulfonate, N-hydroxysuccinimide trifluoromethanesulfonate, N-hydroxysuccinimide ethanesulfonate, N-hydroxysuccinimide 1-propanesulfonate, N-hydroxysuccinimide 2-propanesulfonate, N-hydroxysuccinimide 1-pentanesulfonate, N-hydroxysuccinimide 1-octanesulfonate, N-hydroxysuccinimide p-toluenesulfonate, N-hydroxysuccinimide p-methoxybenzenesulfonate, N-hydroxysuccinimide 2-chloroethanesulfonate, N-hydroxysuccinimide benzenesulfonate, N-hydroxysuccinimide 2,4,6-trimethylbenzenesulfonate, N-hydroxysuccinimide 1-naphthalenesulfonate, N-hydroxysuccinimide 2-naphthalenesulfonate, N-hydroxy-2-phenylsuccinimide methanesulfonate, N-hydroxymaleimide methanesulfonate, N-hydroxymaleimide ethanesulfonate, N-hydroxy-2-phenylmaleimide methanesulfonate, N-hydroxyglutarimide methanesulfonate, N-hydroxyglutarimide benzenesulfonate, N-hydroxyphthalimide methanesulfonate, N-hydroxyphthalimide benzenesulfonate, N-hydroxyphthalimide trifluoromethanesulfonate, N-hydroxyphthalimide p-toluenesulfonate, N-hydroxynaphthalimide methanesulfonate, N-hydroxynaphthalimide benzenesulfonate, N-hydroxy-5-norbornene-2,3-dicarboxyimide methanesulfonate, N-hydroxy-5-norbornene-2,3-dicarboxyimide trifluoromethanesulfonate, and N-hydroxy-5-norbornene-2,3-dicarboxyimide p-toluenesulfonate.

Preferred among these acid generators are onium salts such as triphenylsulfonium trifluoromethanesulfonate, (p-tert-butoxyphenyl)diphenylsulfonium trifluoromethanesulfonate, tris(p-tert-butoxyphenyl)sulfonium trifluoromethanesulfonate, triphenylsulfonium p-toluenesulfonate, (p-tert-butoxyphenyl)diphenylsulfonium p-toluenesulfonate, tris(p-tert-butoxyphenyl)sulfonium p-toluenesulfonate, trinaphthylsulfonium trifluoromethanesulfonate, cyclohexylmethyl(2-oxocyclohexyl)sulfonium trifluoromethanesulfonate, (2-norbornyl)methyl(2-oxocylohexyl)sulfonium trifluoromethanesulfonate, and 1,2′-naphthylcarbonylmethyltetrahydrothiophenium triflate;

diazomethane derivatives such as bis(benzenesulfonyl)diazomethane, bis(p-toluenesulfonyl)diazomethane, bis(cyclohexylsulfonyl)diazomethane, bis(n-butylsulfonyl)diazomethane, bis(isobutylsulfonyl)diazomethane, bis(sec-butylsulfonyl)diazomethane, bis(n-propylsulfonyl)diazomethane, bis(isopropylsulfonyl)diazomethane, and bis(tert-butylsulfonyl)diazomethane;

glyoxime derivatives such as bis-O-(p-toluenesulfonyl)-α-dimethylglyoxime and bis-O-(n-butanesulfonyl)-α-dimethylglyoxime;

bissulfone derivatives such as bisnaphthylsulfonylmethane; and

sulfonic acid esters of N-hydroxyimide compounds such as N-hydroxysuccinimide methanesulfonate, N-hydroxysuccinimide trifluoromethanesulfonate, N-hydroxysuccinimide 1-propanesulfonate, N-hydroxysuccinimide 2-propanesulfonate, N-hydroxysuccinimide 1-pentanesulfonate, N-hydroxysuccinimide p-toluenesulfonate, N-hydroxynaphthalimide methanesulfonate, and N-hydroxynaphthalimide benzenesulfonate.

Also useful are acid generators of the oxime type described in WO 2004/074242 A2.

These acid generators may be used singly or in combinations of two or more thereof. Onium salts are effective for improving rectangularity, while diazomethane derivatives and glyoxime derivatives are effective for reducing standing waves. The combination of an onium salt with a diazomethane or a glyoxime derivative allows for fine adjustment of the profile.

The acid generator is preferably added in an amount of 0.1 to 50 parts, and especially 0.5 to 40 parts by weight, per 100 parts by weight of the base resin. Less than 0.1 phr of the acid generator may generate a less amount of acid upon exposure, sometimes leading to a poor sensitivity and resolution whereas more than 50 phr of the acid generator may adversely affect the transmittance and resolution of resist. For example, where acid generators (P1a-1) and (P1a-2) are used in combination, they are mixed such that the mixture consists of 1 pbw of (P1a-1) and 0.001 to 1 pbw of (P1a-2) because generator (P1a-2) functions only as a thermal acid generator. Differently stated, the amount of thermal acid generator (P1a-2) added is preferably limited to such a level as to have no impact on the lithography of patterning the first resist film, no impact on the thermal properties of the first resist film, and no impact on the second resist film, and specifically to the range of 0.01 to 1 part by weight per 100 parts by weight of the base resin.

Dissolution Inhibitor

To the positive resist composition, especially chemically amplified positive resist composition, a dissolution inhibitor or regulator may be added. The dissolution inhibitor is a compound having on the molecule at least two phenolic hydroxyl groups, in which an average of from 0 to 100 mol % of all the hydrogen atoms on the phenolic hydroxyl groups are replaced with acid labile groups or a compound having on the molecule at least one carboxyl group, in which an average of 50 to 100 mol % of all the hydrogen atoms on the carboxyl groups are replaced with acid labile groups, both the compounds having a weight average molecular weight within a range of 100 to 1,000, and preferably 150 to 800.

The degree of substitution of the hydrogen atoms on the phenolic hydroxyl groups with acid labile groups is on average at least 0 mol %, and preferably at least 30 mol %, of all the phenolic hydroxyl groups. The upper limit is 100 mol %, and preferably 80 mol %. The degree of substitution of the hydrogen atoms on the carboxyl groups with acid labile groups is on average at least 50 mol %, and preferably at least 70 mol %, of all the carboxyl groups, with the upper limit being 100 mol %.

Preferable examples of such compounds having two or more phenolic hydroxyl groups or compounds having at least one carboxyl group include those of formulas (D1) to (D14) below.

In these formulas, R²⁰¹ and R²⁰² are each hydrogen or a straight or branched C₁-C8 alkyl or alkenyl; R²⁰³ is hydrogen, a straight or branched C₁-C8 alkyl or alkenyl, or —(R²⁰⁷)_(h)—COOH; R is —(CH₂)_(i)— (where i=2 to 10), a C₆-C₁₀ arylene, carbonyl, sulfonyl, an oxygen atom, or a sulfur atom; R²⁰⁵ is a C₁-C₁₀ alkylene, a C₆ -C₁₀ arylene, carbonyl, sulfonyl, an oxygen atom, or a sulfur atom; R²⁰⁶ is hydrogen, a straight or branched C₁-C₈ alkyl or alkenyl, or a hydroxyl-substituted phenyl or naphthyl; R²⁰⁷ is a straight or branched C₁-C₁₀ alkylene; R²⁰⁸ is hydrogen or hydroxyl; the letter j is an integer from 0 to 5; u and h are each 0 or 1; s, t, s′, t′, s″, and t″ are each numbers which satisfy s+t=8, s′+t′=5, and s″+t″=4, and are such that each phenyl structure has at least one hydroxyl group; and α is a number such that the compounds of formula (D8) or (D9) have a molecular weight of from 100 to 1,000.

The dissolution inhibitor may be formulated in an amount of 0 to 50 parts, preferably 5 to 50 parts, and more preferably 10 to 30 parts by weight, per 100 parts by weight of the base resin, and may be used singly or as a mixture of two or more thereof. Outside the range, a less amount of the dissolution inhibitor may fail to improve resolution whereas a larger amount may lead to slimming of the patterned film and a decline in resolution.

Basic Compound

The basic compound used herein is preferably a compound capable of suppressing the rate of diffusion when the acid generated by the acid generator diffuses within the resist film. The inclusion of this type of basic compound holds down the rate of acid diffusion within the resist film, resulting in better resolution. In addition, it suppresses changes in sensitivity following exposure, thus reducing substrate and environment dependence, as well as improving the exposure latitude and the pattern profile.

Examples of suitable basic compounds include primary, secondary, and tertiary aliphatic amines, mixed amines, aromatic amines, heterocyclic amines, nitrogen-containing compounds having carboxyl group, nitrogen-containing compounds having sulfonyl group, nitrogen-containing compounds having hydroxyl group, nitrogen-containing compounds having hydroxyphenyl group, nitrogen-containing alcoholic compounds, amide derivatives, and imide derivatives.

Examples of suitable primary aliphatic amines include ammonia, methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, iso-butylamine, sec-butylamine, tert-butylamine, pentylamine, tert-amylamine, cyclopentylamine, hexylamine, cyclohexylamine, heptylamine, octylamine, nonylamine, decylamine, dodecylamine, cetylamine, methylenediamine, ethylenediamine, and tetraethylenepentamine. Examples of suitable secondary aliphatic amines include dimethylamine, diethylamine, di-n-propylamine, di-iso-propylamine, di-n-butylamine, di-iso-butylamine, di-sec-butylamine, dipentylamine, dicyclopentylamine, dihexylamine, dicyclohexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine, didodecylamine, dicetylamine, N,N-dimethylmethylenediamine, N,N-dimethylethylenediamine, and N,N-dimethyltetraethylenepentamine. Examples of suitable tertiary aliphatic amines include trimethylamine, triethylamine, tri-n-propylamine, tri-iso-propylamine, tri-n-butylamine, tri-iso-butylamine, tri-sec-butylamine, tripentylamine, tricyclopentylamine, trihexylamine, tricyclohexylamine, triheptylamine, trioctylamine, trinonylamine, tridecylamine, tridodecylamine, tricetylamine, N,N,N′,N′-tetramethylmethylenediamine, N,N,N′,N′-tetramethylethylenediamine, and N,N,N′,N′-tetramethyltetraethylenepentamine.

Examples of suitable mixed amines include dimethylethylamine, methylethylpropylamine, benzylamine, phenethylamine, and benzyldimethylamine.

Examples of suitable aromatic amines include aniline derivatives (e.g., aniline, N-methylaniline, N-ethylaniline, N-propylaniline, N,N-dimethylaniline, 2-methylaniline, 3-methylaniline, 4-methylaniline, ethylaniline, propylaniline, trimethylaniline, 2-nitroaniline, 3-nitroaniline, 4-nitroaniline, 2,4-dinitroaniline, 2,6-dinitroaniline, 3,5-dinitroaniline, and N,N-dimethyltoluidine), diphenyl(p-tolyl)amine, methyldiphenylamine, triphenylamine, phenylenediamine, naphthylamine, and diaminonaphthalene. Examples of suitable heterocyclic amines include pyrrole derivatives (e.g., pyrrole, 2H-pyrrole, 1-methylpyrrole, 2,4-dimethylpyrrole, 2,5-dimethylpyrrole, and N-methylpyrrole), oxazole derivatives (e.g., oxazole and isooxazole), thiazole derivatives (e.g., thiazole and isothiazole), imidazole derivatives (e.g., imidazole, 4-methylimidazole, and 4-methyl-2-phenylimidazole), pyrazole derivatives, furazan derivatives, pyrroline derivatives (e.g., pyrroline and 2-methyl-1-pyrroline), pyrrolidine derivatives (e.g., pyrrolidine, N-methylpyrrolidine, pyrrolidinone, and N-methylpyrrolidone), imidazoline derivatives, imidazolidine derivatives, pyridine derivatives (e.g., pyridine, methylpyridine, ethylpyridine, propylpyridine, butylpyridine, 4-(1-butylpentyl)pyridine, dimethylpyridine, trimethylpyridine, triethylpyridine, phenylpyridine, 3-methyl-2-phenylpyridine, 4-tert-butylpyridine, diphenylpyridine, benzylpyridine, methoxypyridine, butoxypyridine, dimethoxypyridine, 1-methyl-2-pyridone, 4-pyrrolidinopyridine, 1-methyl-4-phenylpyridine, 2-(1-ethylpropyl)pyridine, aminopyridine, and dimethylaminopyridine), pyridazine derivatives, pyrimidine derivatives, pyrazine derivatives, pyrazoline derivatives, pyrazolidine derivatives, piperidine derivatives, piperazine derivatives, morpholine derivatives, indole derivatives, isoindole derivatives, 1H-indazole derivatives, indoline derivatives, quinoline derivatives (e.g., quinoline and 3-quinolinecarbonitrile), isoquinoline derivatives, cinnoline derivatives, quinazoline derivatives, quinoxaline derivatives, phthalazine derivatives, purine derivatives, pteridine derivatives, carbazole derivatives, phenanthridine derivatives, acridine derivatives, phenazine derivatives, 1,10-phenanthroline derivatives, adenine derivatives, adenosine derivatives, guanine derivatives, guanosine derivatives, uracil derivatives, and uridine derivatives.

Examples of suitable nitrogen-containing compounds having carboxyl group include aminobenzoic acid, indolecarboxylic acid, and amino acid derivatives (e.g., nicotinic acid, alanine, alginine, aspartic acid, glutamic acid, glycine, histidine, isoleucine, glycylleucine, leucine, methionine, phenylalanine, threonine, lysine, 3-aminopyrazine-2-carboxylic acid, and methoxyalanine). Examples of suitable nitrogen-containing compounds having sulfonyl group include 3-pyridinesulfonic acid and pyridinium p-toluenesulfonate. Examples of suitable nitrogen-containing compounds having hydroxyl group, nitrogen-containing compounds having hydroxyphenyl group, and nitrogen-containing alcoholic compounds include 2-hydroxypyridine, aminocresol, 2,4-quinolinediol, 3-indolemethanol hydrate, monoethanolamine, diethanolamine, triethanolamine, N-ethyldiethanolamine, N,N-diethylethanolamine, triisopropanolamine, 2,2′-iminodiethanol, 2-aminoethanol, 3-amino-1-propanol, 4-amino-1-butanol, 4-(2-hydroxyethyl)morpholine, 2-(2-hydroxyethyl)pyridine, 1-(2-hydroxyethyl)piperazine, 1-[2-(2-hydroxyethoxy)ethyl]piperazine, piperidine ethanol, 1-(2-hydroxyethyl)pyrrolidine, 1-(2-hydroxyethyl)-2-pyrrolidinone, 3-piperidino-1,2-propanediol, 3-pyrrolidino-1,2-propanediol, 8-hydroxyjulolidine, 3-quinuclidinol, 3-tropanol, 1-methyl-2-pyrrolidine ethanol, 1-aziridine ethanol, N-(2-hydroxyethyl)phthalimide, and N-(2-hydroxyethyl)isonicotinamide.

Examples of suitable amide derivatives include formamide, N-methylformamide, N,N-dimethylformamide, acetamide, N-methylacetamide, N,N-dimethylacetamide, propionamide, and benzamide. Suitable imide derivatives include phthalimide, succinimide, and maleimide.

One or more basic compounds of the following general formula (B)-1 may also be added.

N(X)_(n)(Y)_(3-n)   (B)-1

In the formula, n is equal to 1, 2 or 3; side chain Y is independently hydrogen or a straight, branched or cyclic alkyl group of 1 to 20 carbon atoms which may contain an ether or hydroxyl group; and side chain X is independently selected from groups of the following general formulas (X)-1 to (X)-3, and two or three X's may bond together to form a ring with the nitrogen atom to which they are attached.

In the formulas, R³⁰⁰, R³⁰² and R³⁰⁵ are independently straight or branched alkylene groups of 1 to 4 carbon atoms; R³⁰¹ and R³⁰⁴ are independently hydrogen, straight, branched or cyclic alkyl groups of 1 to 20 carbon atoms, which may contain at least one hydroxyl, ether, ester group or lactone ring; R³⁰³ is a single bond or a straight or branched alkylene group of 1 to 4 carbon atoms; and R³⁰⁶ is a straight, branched or cyclic alkyl group of 1 to 20 carbon atoms, which may contain at least one hydroxyl, ether, ester group or lactone ring.

Illustrative examples of the compounds of formula (B)-1 include tris(2-methoxymethoxyethyl)amine, tris{2-(2-methoxyethoxy)ethyl}amine, tris{2-(2-methoxyethoxymethoxy)ethyl}amine, tris{2-(1-methoxyethoxy)ethyl}amine, tris{2-(1-ethoxyethoxy)ethyl}amine, tris{2-(1-ethoxypropoxy)ethyl}amine, tris[2-{2-(2-hydroxyethoxy)ethoxy}ethyl]amine, 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane, 4,7,13,18-tetraoxa-1,10-diazabicyclo[8.5.5]eicosane, 1,4,10,13-tetraoxa-7,16-diazabicyclooctadecane, 1-aza-12-crown-4, 1-aza-15-crown-5, 1-aza-18-crown-6, tris(2-formyloxyethyl)amine, tris(2-acetoxyethyl)amine, tris(2-propionyloxyethyl)amine, tris(2-butyryloxyethyl)amine, tris(2-isobutyryloxyethyl)amine, tris(2-valeryloxyethyl)amine, tris(2-pivaloyloxyethyl)amine, N,N-bis(2-acetoxyethyl)-2-(acetoxyacetoxy)ethylamine, tris(2-methoxycarbonyloxyethyl)amine, tris(2-tert-butoxycarbonyloxyethyl)amine, tris[2-(2-oxopropoxy)ethyl]amine, tris[2-(methoxycarbonylmethyl)oxyethyl]amine, tris[2-(tert-butoxycarbonylmethyloxy)ethyl]amine, tris[2-(cyclohexyloxycarbonylmethyloxy)ethyl]amine, tris(2-methoxycarbonylethyl)amine, tris(2-ethoxycarbonylethyl)amine, N,N-bis(2-hydroxyethyl)-2-(methoxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(methoxycarbonyl)ethylamine, N,N-bis(2-hydroxyethyl)-2-(ethoxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(ethoxycarbonyl)ethylamine, N,N-bis(2-hydroxyethyl)-2-(2-methoxyethoxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(2-methoxyethoxycarbonyl)ethylamine, N,N-bis(2-hydroxyethyl)-2-(2-hydroxyethoxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(2-acetoxyethoxycarbonyl)ethylamine, N,N-bis(2-hydroxyethyl)-2-[(methoxycarbonyl)methoxycarbonyl]ethylamine, N,N-bis(2-acetoxyethyl)-2-[(methoxycarbonyl)methoxycarbonyl]ethylamine, N,N-bis(2-hydroxyethyl)-2-(2-oxopropoxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(2-oxopropoxycarbonyl)ethylamine, N,N-bis(2-hydroxyethyl)-2-(tetrahydrofurfuryloxycarbonyl)ethylamine, N,N-bis(2-acetoxyethyl)-2-(tetrahydrofurfuryloxycarbonyl)ethylamine, N,N-bis(2-hydroxyethyl)-2-[(2-oxotetrahydrofuran-3-yl)oxycarbonyl]ethylamine, N,N-bis(2-acetoxyethyl)-2-[(2-oxotetrahydrofuran-3-yl)oxycarbonyl]ethylamine, N,N-bis(2-hydroxyethyl)-2-(4-hydroxybutoxycarbonyl)ethylamine, N,N-bis(2-formyloxyethyl)-2-(4-formyloxybutoxycarbonyl)ethylamine, N,N-bis(2-formyloxyethyl)-2-(2-formyloxyethoxycarbonyl)ethylamine, N,N-bis(2-methoxyethyl)-2-(methoxycarbonyl)ethylamine, N-(2-hydroxyethyl)-bis[2-(methoxycarbonyl)ethyl]amine, N-(2-acetoxyethyl)-bis[2-(methoxycarbonyl)ethyl]amine, N-(2-hydroxyethyl)-bis[2-(ethoxycarbonyl)ethyl]amine, N-(2-acetoxyethyl)-bis[2-(ethoxycarbonyl)ethyl]amine, N-(3-hydroxy-1-propyl)-bis[2-(methoxycarbonyl)ethyl]amine, N-(3-acetoxy-1-propyl)-bis[2-(methoxycarbonyl)ethyl]amine, N-(2-methoxyethyl)-bis[2-(methoxycarbonyl)ethyl]amine, N-butyl-bis[2-(methoxycarbonyl)ethyl]amine, N-butyl-bis[2-(2-methoxyethoxycarbonyl)ethyl]amine, N-methyl-bis(2-acetoxyethyl)amine, N-ethyl-bis(2-acetoxyethyl)amine, N-methyl-bis(2-pivaloyloxyethyl)amine, N-ethyl-bis[2-(methoxycarbonyloxy)ethyl]amine, N-ethyl-bis[2-(tert-butoxycarbonyloxy)ethyl]amine, tris(methoxycarbonylmethyl)amine, tris(ethoxycarbonylmethyl)amine, N-butyl-bis(methoxycarbonylmethyl)amine, N-hexyl-bis(methoxycarbonylmethyl)amine, and β-(diethylamino)-δ-valerolactone.

Also useful are basic compounds having cyclic structure, represented by the following general formula (B)-2.

Herein X is as defined above, and R³⁰⁷ is a straight or branched alkylene group of 2 to 20 carbon atoms which may contain one or more carbonyl, ether, ester or sulfide groups.

Illustrative examples of the compounds having formula (B)-2 include 1-[2-(methoxymethoxy)ethyl]pyrrolidine, 1-[2-(methoxymethoxy)ethyl]piperidine, 4-[2-(methoxymethoxy)ethyl]morpholine, 1-[2-[(2-methoxyethoxy)methoxy]ethyl]pyrrolidine, 1-[2-[(2-methoxyethoxy)methoxy]ethyl]piperidine, 4-[2-[(2-methoxyethoxy)methoxy]ethyl]morpholine, 2-(1-pyrrolidinyl)ethyl acetate, 2-piperidinoethyl acetate, 2-morpholinoethyl acetate, 2-(1-pyrrolidinyl)ethyl formate, 2-piperidinoethyl propionate, 2-morpholinoethyl acetoxyacetate, 2-(1-pyrrolidinyl)ethyl methoxyacetate, 4-[2-(methoxycarbonyloxy)ethyl]morpholine, 1-[2-(t-butoxycarbonyloxy)ethyl]piperidine, 4-[2-(2-methoxyethoxycarbonyloxy)ethyl]morpholine, methyl 3-(1-pyrrolidinyl)propionate, methyl 3-piperidinopropionate, methyl 3-morpholinopropionate, methyl 3-(thiomorpholino)propionate, methyl 2-methyl-3-(1-pyrrolidinyl)propionate, ethyl 3-morpholinopropionate, methoxycarbonylmethyl 3-piperidinopropionate, 2-hydroxyethyl 3-(1-pyrrolidinyl)propionate, 2-acetoxyethyl 3-morpholinopropionate, 2-oxotetrahydrofuran-3-yl 3-(1-pyrrolidinyl)propionate, tetrahydrofurfuryl 3-morpholinopropionate, glycidyl 3-piperidinopropionate, 2-methoxyethyl 3-morpholinopropionate, 2-(2-methoxyethoxy)ethyl 3-(1-pyrrolidinyl)propionate, butyl 3-morpholinopropionate, cyclohexyl 3-piperidinopropionate, α-(1-pyrrolidinyl)methyl-γ-butyrolactone, β-piperidino-γ-butyrolactone, β-morpholino-δ-valerolactone, methyl 1-pyrrolidinylacetate, methyl piperidinoacetate, methyl morpholinoacetate, methyl thiomorpholinoacetate, ethyl 1-pyrrolidinylacetate, and 2-methoxyethyl morpholinoacetate.

Also, basic compounds having cyano group, represented by the following general formulae (B)-3 to (B)-6 are useful.

Herein, X, R³⁰⁷ and n are as defined above, and R³⁰⁸ and R³⁰⁹ are each independently a straight or branched alkylene group of 1 to 4 carbon atoms.

Illustrative examples of the basic compounds having cyano group, represented by formulae (B)-3 to (B)-6, include 3-(diethylamino)propiononitrile, N,N-bis(2-hydroxyethyl)-3-aminopropiononitrile, N,N-bis(2-acetoxyethyl)-3-aminopropiononitrile, N,N-bis(2-formyloxyethyl)-3-aminopropiononitrile, N,N-bis(2-methoxyethyl)-3-aminopropiononitrile, N,N-bis[2-(methoxymethoxy)ethyl]-3-aminopropiononitrile, methyl N-(2-cyanoethyl)-N-(2-methoxyethyl)-3-aminopropionate, methyl N-(2-cyanoethyl)-N-(2-hydroxyethyl)-3-aminopropionate, methyl N-(2-acetoxyethyl)-N-(2-cyanoethyl)-3-aminopropionate, N-(2-cyanoethyl)-N-ethyl-3-aminopropiononitrile, N-(2-cyanoethyl)-N-(2-hydroxyethyl)-3-aminopropiononitrile, N-(2-acetoxyethyl)-N-(2-cyanoethyl)-3-aminopropiononitrile, N-(2-cyanoethyl)-N-(2-formyloxyethyl)-3-aminopropiononitrile, N-(2-cyanoethyl)-N-(2-methoxyethyl)-3-aminopropiononitrile, N-(2-cyanoethyl)-N-[2-(methoxymethoxy)ethyl]-3-aminopropiononitrile, N-(2-cyanoethyl)-N-(3-hydroxy-1-propyl)-3-aminopropiononitrile, N-(3-acetoxy-1-propyl)-N-(2-cyanoethyl)-3-aminopropiononitrile, N-(2-cyanoethyl)-N-(3-formyloxy-1-propyl)-3-aminopropiononitrile, N-(2-cyanoethyl)-N-tetrahydrofurfuryl-3-aminopropiononitrile, N,N-bis(2-cyanoethyl)-3-aminopropiononitrile, diethylaminoacetonitrile, N,N-bis(2-hydroxyethyl)aminoacetonitrile, N,N-bis(2-acetoxyethyl)aminoacetonitrile, N,N-bis(2-formyloxyethyl)aminoacetonitrile, N,N-bis(2-methoxyethyl)aminoacetonitrile, N,N-bis[2-(methoxymethoxy)ethyl]aminoacetonitrile, methyl N-cyanomethyl-N-(2-methoxyethyl)-3-aminopropionate, methyl N-cyanomethyl-N-(2-hydroxyethyl)-3-aminopropionate, methyl N-(2-acetoxyethyl)-N-cyanomethyl-3-aminopropionate, N-cyanomethyl-N-(2-hydroxyethyl)aminoacetonitrile, N-(2-acetoxyethyl)-N-(cyanomethyl)aminoacetonitrile, N-cyanomethyl-N-(2-formyloxyethyl)aminoacetonitrile, N-cyanomethyl-N-(2-methoxyethyl)aminoacetonitrile, N-cyanomethyl-N-[2-(methoxymethoxy)ethyl]aminoacetonitrile, N-cyanomethyl-N-(3-hydroxy-1-propyl)aminoacetonitrile, N-(3-acetoxy-1-propyl)-N-(cyanomethyl)aminoacetonitrile, N-cyanomethyl-N-(3-formyloxy-1-propyl)aminoacetonitrile, N,N-bis(cyanomethyl)aminoacetonitrile, 1-pyrrolidinepropiononitrile, 1-piperidinepropiononitrile, 4-morpholinepropiononitrile, 1-pyrrolidineacetonitrile, 1-piperidineacetonitrile, 4-morpholineacetonitrile, cyanomethyl 3-diethylaminopropionate, cyanomethyl N,N-bis(2-hydroxyethyl)-3-aminopropionate, cyanomethyl N,N-bis(2-acetoxyethyl)-3-aminopropionate, cyanomethyl N,N-bis(2-formyloxyethyl)-3-aminopropionate, cyanomethyl N,N-bis(2-methoxyethyl)-3-aminopropionate, cyanomethyl N,N-bis[2-(methoxymethoxy)ethyl]-3-aminopropionate, 2-cyanoethyl 3-diethylaminopropionate, 2-cyanoethyl N,N-bis(2-hydroxyethyl)-3-aminopropionate, 2-cyanoethyl N,N-bis(2-acetoxyethyl)-3-aminopropionate, 2-cyanoethyl N,N-bis(2-formyloxyethyl)-3-aminopropionate, 2-cyanoethyl N,N-bis(2-methoxyethyl)-3-aminopropionate, 2-cyanoethyl N,N-bis[2-(methoxymethoxy)ethyl]-3-aminopropionate, cyanomethyl 1-pyrrolidinepropionate, cyanomethyl 1-piperidinepropionate, cyanomethyl 4-morpholinepropionate, 2-cyanoethyl 1-pyrrolidinepropionate, 2-cyanoethyl 1-piperidinepropionate, and 2-cyanoethyl 4-morpholinepropionate.

The basic compound is preferably formulated in an amount of 0.001 to 2 parts, and especially 0.01 to 1 part by weight, per 100 parts by weight of the base resin. Less than 0.001 phr of the basic compound achieves no or little addition effect whereas more than 2 phr would result in too low a sensitivity.

Other Components

Also, a polymer comprising recurring units having amino and fluoroalkyl groups may be added. This polymer orients or segregates at the resist surface after coating, preventing the resist pattern as developed from slimming and improving rectangularity. For preventing pattern slimming, the addition of the following polymer is effective.

Herein R⁰¹, R⁰⁴, and R⁰⁷ are each independently hydrogen or methyl. X¹, Y¹ and Y² are each independently a single bond, —O—R⁰⁹—, —C(═O)—O—R⁰⁹—, —C(═O)—NH—R⁰⁹—, a straight or branched C₁-C₄ alkylene, or phenylene group, wherein R⁰⁹ is a straight, branched or cyclic C₁-C₁₀ alkylene group which may contain an ester (—COO—) or ether (—O—) group. The subscript n is 1 or 2. In case of n=1, Y¹ is a single bond, —O—R⁰⁹—, —C(═O)—O—R⁰⁹—, —C(═O)—NH—R⁰¹⁰—, a straight or branched C₁-C₄ alkylene, or phenylene group, wherein R⁰⁹ is as defined above. In case of n=2, Y¹ is —O—R⁰¹⁰═, —C(═O)—O—R⁰¹⁰═, —C(═O)—NH—R⁰¹⁰═, a straight or branched C₁-C₄ alkylene group with one hydrogen atom eliminated, or a phenylene group with one hydrogen atom eliminated, wherein R⁰¹⁰ is a straight, branched or cyclic C₁-C₁₀ alkylene group with one hydrogen atom eliminated which may contain an ester or ether group. R⁰² and R⁰³ are each independently hydrogen, a straight, branched or cyclic C₁-C₂₀ alkyl or C₂-C₂₀ alkenyl group which may contain a hydroxy, ether, ester, cyano, amino group, double bond or halogen atom, or a C₆-C₁₀ aryl group, or R⁰² and R⁰³ may bond together to form a ring of 3 to 20 carbon atoms with the nitrogen atom to which they are attached. R⁰⁵ is a straight, branched or cyclic C₁-C₁₂ alkylene group. R⁰⁶ is hydrogen, fluorine, methyl, trifluoromethyl or difluoromethyl, or R⁰⁶ and R⁰⁵ may bond together to form an alicyclic ring of 2 to 12 carbon atoms with the carbon atom to which they are attached, which ring may contain an ether group, fluorinated alkylene group or trifluoromethyl group. R⁰⁸ is a straight, branched or cyclic C₁-C₂₀ alkyl group which has at least one fluorine atom substituted thereon and which may contain an ether, ester or sulfonamide group. The subscripts (a-1), (b-1), and (b-2) are numbers in the range: 0<(a-1)<1.0, 0≦(b-1)<1.0, 0≦(b-2)<1.0, 0<(b-1)+(b-2)<1.0, and 0.5≦(a-1)+(b-1)+(b-2)≦1.0.

In the positive resist composition, a compound having a group ≡C—COOH in the molecule may be blended. Exemplary, non-limiting compounds having a carboxyl group include one or more compounds selected from Groups I and II below. Including this compound improves the post-exposure delay (PED) stability of the resist and ameliorates edge roughness on nitride film substrates.

Group I:

Compounds of general formulas (A1) to (A10) below in which some or all of the hydrogen atoms on the phenolic hydroxyl groups have been replaced by —R⁴⁰¹—COOH (wherein R⁴⁰¹ is a straight or branched alkylene of 1 to 10 carbon atoms), and in which the molar ratio C/(C+D) of phenolic hydroxyl groups (C) to ≡C—COOH groups (D) in the molecule is from 0.1 to 1.0.

In these formulas, R⁴⁰⁸ is hydrogen or methyl; R⁴⁰² and R⁴⁰³ are each hydrogen or a straight or branched C₁-C₈ alkyl or alkenyl; R⁴⁰⁴ is hydrogen, a straight or branched C₁-C₈ alkyl or alkenyl, or a —(R⁴⁰⁹)_(h)—COOR′ group (R′ being hydrogen or —R⁴⁰⁹—COOH); R⁴⁰⁵ is —(CH₂)_(i)— (wherein i is 2 to 10), a C₆-C₁₀ arylene, carbonyl, sulfonyl, an oxygen atom, or a sulfur atom; R⁴⁰⁶ is a C₁-C₁₀ alkylene, a C₆ -C₁₀ arylene, carbonyl, sulfonyl, an oxygen atom, or a sulfur atom; R⁴⁰⁹ is hydrogen, a straight or branched C₁-C₈ alkyl or alkenyl, or a hydroxyl-substituted phenyl or naphthyl; R⁴⁰⁹ is a straight or branched C₁-C₁₀ alkyl or alkenyl or a —R⁴¹¹—COOH group; R⁴¹⁰ is hydrogen, a straight or branched C₁-C₈ alkyl or alkenyl, or a —R⁴¹¹—COOH group; R⁴¹¹ is a straight or branched C₁-C₁₀ alkylene; h is an integer of 1 to 4, j is an integer from 0 to 3; s1, t1, s2, t2, s3, t3, s4, and t4 are each numbers which satisfy s1+t1 =8, s2+t2=5, s3+t3=4, and s4+t4=6, and are such that each phenyl structure has at least one hydroxyl group; u is an integer of 1 to 4; κ is a number such that the compound of formula (A6) may have a weight average molecular weight of 1,000 to 5,000; and λ is a number such that the compound of formula (A7) may have a weight average molecular weight of 1,000 to 10,000.

Group II:

Compounds of general formulas (A11) to (A15) below.

In these formulas, R⁴⁰², R⁴⁰³, and R⁴¹¹ are as defined above; R⁴¹² is hydrogen or hydroxyl; s5 and t5 are numbers which satisfy s5≧0, t5≧0, and s5+t5=5; and h′ is 0 or 1.

Illustrative, non-limiting examples of the compound having a carboxyl group include compounds of the general formulas (AI-1) to (AI-14) and (AII-1) to (AII-10) below.

In the above formulas, R″ is hydrogen or a —CH₂COOH group such that the —CH₂COOH group accounts for 10 to 100 mol % of R″ in each compound, κ and λ are as defined above.

The carboxyl compound is added in an amount ranging from 0 to 5 parts, preferably 0.1 to 5 parts, more preferably 0.1 to 3 parts, further preferably 0.1 to 2 parts by weight, per 100 parts by weight of the base resin. More than 5 phr of the compound may reduce the resolution of the resist composition.

The positive resist composition used herein may further include a surfactant for improving the coating characteristics.

Illustrative, non-limiting, examples of the surfactant include nonionic surfactants, for example, polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, polyoxyethylene cetyl ether, and polyoxyethylene oleyl ether, polyoxyethylene alkylaryl ethers such as polyoxyethylene octylphenol ether and polyoxyethylene nonylphenol ether, polyoxyethylene polyoxypropylene block copolymers, sorbitan fatty acid esters such as sorbitan monolaurate, sorbitan monopalmitate, and sorbitan monostearate, and polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan trioleate, and polyoxyethylene sorbitan tristearate; fluorochemical surfactants such as EFTOP EF301, EF303 and EF352 (Tohkem Products Co., Ltd.), Megaface F171, F172 and F173 (Dai-Nippon Ink & Chemicals, Inc.), Fluorad FC-430, FC-431 and FC-4430 (Sumitomo 3M Co., Ltd.), Asahiguard AG710, Surflon S-381, S-382, SC101, SC102, SC103, SC104, SC105, SC106, Surfynol E1004, KH-10, KH-20, KH-30 and KH-40 (Asahi Glass Co., Ltd.); organosiloxane polymers KP-341, X-70-092 and X-70-093 (Shin-Etsu Chemical Co., Ltd.), acrylic acid or methacrylic acid Polyflow No. 75 and No. 95 (Kyoeisha Ushi Kagaku Kogyo Co., Ltd.). Inter alia, FC-430, FC-4430, Surflon S-381, Surfynol E1004, KH-20 and KH-30 are preferred. These surfactants may be used alone or in admixture.

To the positive resist composition, the surfactant is added in an amount of up to 2 parts, preferably up to 1 part by weight, per 100 parts by weight of the base resin.

Second Resist Composition

The second positive resist composition from which a second resist film serving as a reversal film in the double pattern forming process of the invention is formed comprises as a base resin a polymer comprising recurring units having an alkali-soluble group protected with an acid labile group which is eliminatable with acid. Preferably the polymer comprises recurring units having a lactone ring and recurring units having an alkali-soluble group protected with an acid labile group which is eliminatable with acid. More preferably the recurring units having an alkali-soluble group protected with an acid labile group which is eliminatable with acid are recurring units of the general formula (c):

wherein R⁸ is hydrogen or methyl, R⁹ is an acid labile group, and c is a number in the range: 0<c≦0.8.

The monomers from which recurring units of formula (c) are derived are monomers Mc of the following formula wherein R⁸ and R⁹ are as defined above.

The acid labile group represented by R⁹ in formula (c) may be selected from a variety of such groups, specifically groups of formulae (AL-10) and (AL-11), tertiary alkyl groups of formula (AL-12), and oxoalkyl groups of 4 to 20 carbon atoms, as previously illustrated for the acid labile groups in the first resist composition. Exemplary acid labile groups are the same as exemplified previously.

While the polymer used in the second positive resist composition preferably includes recurring units of formula (c), it may have copolymerized therein recurring units (d) derived from monomers having adhesive groups such as hydroxy, cyano, carbonyl, ester, ether groups, lactone rings, carbonyl groups or carboxylic anhydride groups. Examples of recurring units (d) are the same as exemplified previously in connection with the first positive resist composition.

In the polymer, the recurring units (c) and (d) are present in proportions c and d, respectively, which satisfy the range: 0<c≦0.8 and 0≦d<1.0, and preferably 0.1≦c≦0.7 and 0≦d≦0.9, provided that c+d=1.

It is noted that the meaning of c+d=1 is that in a polymer comprising recurring units (c) and (d), the sum of recurring units (c) and (d) is 100 mol % based on the total amount of entire recurring units.

The base resin in the second positive resist composition from which a second resist film serving as a reversal film in the double pattern forming process of the invention is formed may also include phenolic polymers as used in KrF, EB and EUV lithography processes. A number of resist materials comprising phenolic polymers have been proposed. Use may be made of the resist materials described in the following patent references.

JP-A 10-207066 JP-A 10-020504 JP-A 10-265524 JP-A 2001-324814 JP-A 2002-202610 JP-A 2002-234910 JP-A 2002-244297 JP-A 2002-107934 JP-A 2002-107933 JP-A 2003-84440 JP-A 2003-131384 JP-A 2004-45448 JP-A 2004-61794 JP-A 2004-115630 JP-A 2004-149756 JP-A 2004-348014 JP-A 2005-8766 JP-A 2005-8769 JP-A 2006-169302 JP-A 2007-114728 JP-A 2007-132998 JP-A 2007-254494 JP-A 2007-254495 JP-A 2007-270128 JP-A 2008-50568 JP-A 2008-95009

The polymer serving as the base resin in the second resist material used in the double pattern forming process of the invention should preferably have a weight average molecular weight (Mw) in the range of 2,000 to 30,000, as measured by gel permeation chromatography (GPC) using polystyrene standards. A polymer with too low a Mw may allow for substantial acid diffusion during PEB, leading to degraded resolution. With too high a Mw, it may be difficult to embed the second resist material close between features of the first resist pattern, and the polymer may lose alkali solubility and give rise to a footing phenomenon after pattern formation.

If a polymer used in the second resist material (like the polymer in the first resist material) has a wide molecular weight distribution or dispersity (Mw/Mn), which indicates the presence of lower and higher molecular weight polymer fractions, there is a possibility that foreign matter is left on the pattern or the pattern profile is degraded. The influences of molecular weight and dispersity become stronger as the pattern rule becomes finer. Therefore, the multi-component copolymer should preferably have a narrow dispersity (Mw/Mn) of 1.0 to 2.0, especially 1.0 to 1.5, in order to provide a resist composition suitable for micropatterning to a small feature size.

It is understood that a blend of two or more polymers which differ in compositional ratio, molecular weight or dispersity is acceptable.

The polymer as used herein may be synthesized by any desired method, for example, by dissolving unsaturated bond-containing monomers corresponding to the respective units (c) and (d) in an organic solvent, adding a radical initiator thereto, and effecting heat polymerization. Examples of the organic solvent which can be used for polymerization include toluene, benzene, tetrahydrofuran, diethyl ether and dioxane. Examples of the polymerization initiator used herein include 2,2′-azobisisobutyronitrile (AIBN), 2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl 2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide. Preferably the system is heated at 50 to 80° C. for polymerization to take place. The reaction time is 2 to 100 hours, preferably 5 to 20 hours. The acid labile group that has been incorporated in the monomers may be kept as such, or the acid labile group may be once removed with an acid catalyst and thereafter protected or partially protected.

The base resin in the second positive resist composition used in the double pattern forming process of the invention may also include polysiloxane compounds, specifically polysiloxane compounds comprising structural units having the general formulae (1) and (2) and further comprising third structural units having the general formula (3).

Herein R¹⁰ is a C₃-C₂₀ monovalent organic group of straight, branched, cyclic or polycyclic structure which has a hydroxyl group on a carbon atom as a functional group, which has in total at least three fluorine atoms substituted on carbon atoms bonded to the hydroxyl-bonded carbon atom, and which may contain one or more halogen, oxygen or sulfur atom in addition to the fluorine atoms. R¹ is a C₁-C₆ monovalent hydrocarbon group of straight, branched or cyclic structure. R¹² is a C₃-C₂₀ monovalent organic group of straight, branched, cyclic or polycyclic structure which has a carboxyl group protected with an acid labile protective group as a functional group, and which may contain one or more halogen, oxygen or sulfur atom in addition to the carboxyl group. R¹³ is as defined for R¹¹. R¹⁴ is a C₄-C₁₆ monovalent organic group which has a lactone ring as a functional group and which may contain one or more halogen, oxygen or sulfur atom in addition to the lactone ring. R¹⁵ is as defined for R¹¹. The subscript p is 0 or 1, q is 0 or 1, and r is 0 or 1.

The unit having formula (1) is incorporated as a structural unit having a polar group capable of controlling swell. It contributes to this effect that unlike ordinary alcohols, the hydroxyl group on R¹⁰ affords an adequate acidity because the density of electrons on oxygen is reduced due to the strong attraction of electrons by fluorine atoms bonded at adjacent positions. Fluorine atoms exert a substantial electron attracting effect when they are bonded to a carbon atom which is bonded to the hydroxyl-bonded carbon atom, but less such effect when bonded at a remoter position. To acquire this effect more efficiently, it is preferred to attach a trifluoromethyl group(s) to the hydroxyl-bonded carbon atom. A typical partial structure is hexafluoroisopropyl group. A number of such fluorine-substituted alcohol derivatives have already been reported. A silicone structural unit can be obtained by effecting hydrosilylation between such an alcohol derivative having an unsaturated bond and a silane to form a silane monomer, followed by hydrolytic condensation. The skeleton of substituent group forming the side chain is a C₃-C₂₀ organic group of straight, branched, cyclic or polycyclic structure which may contain a halogen, oxygen or sulfur atom(s). Several of fluorinated silicone compounds having a hydroxyl group have already been disclosed (e.g., in JP-A 2002-268227 and JP-A 2003-173027) and they all can be generally used herein. Of the structural units belonging to this genus, a choice of a single unit may be made or a mixture of two or more different units may be used. Of these units, use of a structural unit having a norbornane skeleton is advantageous in purification or the like because the resulting resin is most likely solid. Some typical examples are given below.

Of the structural units having formula (1), polysiloxane compounds having the following formula (Si-10) are preferred.

In the structural unit having formula (2), R¹² is a side chain having carboxylic acid protected with an acid labile group, which functions to establish differential dissolution between exposed and unexposed areas. The acid labile group is a technical term generally used in the resist-related art. The acid labile group with which a functional group is protected functions such that when a strong acid is generated from a photoacid generator upon exposure, the bond between the acid labile group and the functional group is scissored under the catalysis of the strong acid. As a result of scission, carboxylic acid is regenerated herein. The protective group used herein may be any of well-known groups. When carboxylic acid is to be protected, the preferred protective groups are C₄-C₂₀ tertiary alkyl groups, C₃-C18 trialkylsilyl groups, and C₄-C₂₀ oxoalkyl groups. Of the tertiary alkyl groups, those tertiary alkyl groups in which substituent groups on a tertiary carbon atom are substituted so as to form a 5- to 7-membered ring with that tertiary carbon and those tertiary alkyl groups in which a carbon chain bonded to a tertiary carbon atom has a branched or cyclic structure are most preferred because they afford high resolution.

The side chain bearing carboxylic acid to be protected is a C₃ -C₂₀ organic group of straight, branched, cyclic or polycyclic structure which may contain a halogen, oxygen or sulfur atom(s). As in the previous case, this is also readily obtainable by effecting hydrosilylation of a protected carboxylic acid derivative having an unsaturated carbon bond with a silane to form a silicone monomer, followed by hydrolytic condensation. Of these, those monomers in which both silicon and a protected carboxyl group are in direct bond with a norbornane ring or tetracyclododecene ring are most preferred because they afford high resolution. Of the structural units having formula (2), those having the following formula (Si-11) are preferred.

Herein R¹⁶ is an acid labile group, and n is an integer of 0 or 1.

Preferred examples of the acid labile group represented by R¹⁶ are given below.

Like the unit of formula (1), for the unit of formula (2), a single unit or a mixture of different units belonging to this genus may be used.

The unit of formula (3) ensures that the silicone resin has a necessary polarity and serves as a second polar group functioning to reduce the necessary quantity of the unit of formula (2). With respect to the polar group, a number of polar groups including hydroxy, carbonyloxyalkyl, carboxyl and carbonate groups have already been disclosed. An actual attempt to combine the unit of formula (1) with the unit of formula (2) failed to provide such an effect as exerted by acrylic acid polymers for the single layer use, that is, failed to provide high resolution. By contrast, the additional use of the lactone skeleton-bearing unit having formula (3) is successful in establishing both polarity and high resolution.

The silicone structure having a lactone skeleton which have been reported include those structures having lactone incorporated in a cyclic structure, those structures having a linker, and those structures in which lactone is linked to a cyclic structure via a linker (see JP-A 2002-268227). Of these, the structural units having a cycloaliphatic skeleton and further a five-membered lactone skeleton bonded thereto, and having a side chain in which a silicon atom is bonded to one of carbon atoms within the cycloaliphatic skeleton are most preferred because the highest resolution is accomplished.

Two structural units (i.e., silicone side chains) affording the best resolution are illustrated below.

Herein Y is an oxygen atom, sulfur atom or methylene group, and m is 0 or 1.

Of the above-illustrated compounds of formula (Si-12), those side chains wherein Y is oxygen are more preferred for use in the inventive composition because of a more polar effect. Of the above-illustrated compounds of formula (Si-13), those compounds wherein m is 0 and those compounds wherein m is 1 may be used alone or in admixture.

Like the units of formulae (1) and (2), for the unit of formula (3), a single unit or a mixture of different units belonging to this genus may be used.

The structural units having formulae (1), (2) and (3) may be either divalent structural units or trivalent silicone compounds. The situation where p, q or r is 0 means trivalent and the situation where p, q or r is 1 means divalent. When divalent structural units account for 50 mol % or more based on the entire structural units of formulae (1), (2) and (3), a silicone resin resulting from condensation of these monomers is unlikely to solidify and thus difficult to purify. Thus, trivalent structural units are preferably included in an amount of at least 50 mol %.

When the divalent monomer is used, the other side chain R¹¹, R¹³ or R¹⁵ from silicon may be selected from simple groups because no particular function is assigned thereto. Since a carbon number in excess of 6 tends to interfere with purification by distillation or the like, a choice is preferably made of hydrocarbon groups having not more than 6 carbon atoms.

With respect to the proportion of structural units having formulae (1), (2) and (3), first of all, the ratio of the structural unit of formula (2) to the entire silicone structural units is determined because a dissolution contrast between exposed and unexposed areas of a resist coating is almost dictated by this ratio. The ratio of the structural unit of formula (2) is preferably 5 to 80 mol %, more preferably 10 to 50 mol %, based on the entire polysiloxane compound although it varies somewhat with the molecular weight of the protecting group or the like.

Next, the total amount of polar groups, that is, the total amount of the structural units of formulae (1) and (3) is preferably 20 to 95 mol %, more preferably 50 to 90 mol %, based on the entire polysiloxane compound. If these units are in short, the resist pattern can collapse by peeling and swelling during development. If these units are in excess, the resist coating may have a lower contrast and lower resolution.

With respect to the ratio of the structural unit of formula (1) to the structural unit of formula (3), if one structural unit is less than 10 mol % based on the total of these two structural units, the function of the one structural unit is not available. It is thus preferred that each structural unit be 10 to 90 mol % based on the total of structural units of formulae (1) and (3).

Further, divalent or more siloxane units other than the structural units of formulae (1) to (3) may be added as long as their amount is at most 30 mol % of the entire polysiloxane compound. For example, where every siloxane structural unit has a bulky side chain, in some cases, only a compound with a lower molecular weight can be obtained through mere adjustment of condensation conditions for polysiloxane synthesis. In such cases, the molecular weight can be increased by adding units having only an alkyl group of at most 4 carbon atoms, typically methylsiloxane. Also, where it is desired to enhance the transparency of a resin to exposure light of shorter wavelength, typically light of 157 nm, it is known effective to increase the number of fluorine atoms contained in the resin per unit weight. For imparting such transparency to the resist of the invention, it is effective to introduce siloxane units having fluoroalkyl groups introduced therein.

These siloxane structure units can be synthesized by cohydrolytic condensation of a mixture of hydrolyzable silane compounds corresponding to the respective units, i.e., by contacting a mixture of silane monomers with water. The reaction may be effected in the presence of an acid catalyst or base catalyst and also in an organic solvent. Examples of suitable acid catalysts used in the reaction include hydrochloric acid, nitric acid, acetic acid, oxalic acid, sulfuric acid, methanesulfonic acid, p-toluenesulfonic acid, trifluoroacetic acid, trifluoromethanesulfonic acid, perchloric acid, phosphoric acid and citric acid. Examples of suitable base catalysts include ammonia, methylamine, dimethylamine, ethylamine, diethylamine, triethylamine, sodium hydroxide, potassium hydroxide, tetramethylammonium hydroxide, tetrapropylammonium hydroxide, choline, diethylhydroxylamine, DBU, and DBN. Suitable organic solvents include polar solvents such as ethanol, IPA, MIBK, acetonitrile, DMA, and DMF, and aromatic solvents such as benzene, toluene, and xylene, which may be used alone or in admixture.

The silicone resin or polysiloxane compound produced as the cohydrolytic condensate of a mixture of silane monomers should preferably have a weight average molecular weight (Mw) of 1,000 to 100,000, more preferably 1,000 to 30,000, and even more preferably 1,500 to 20,000, as measured by GPC versus polystyrene standards. Resins having a Mw in excess of 100,000 may be difficult to purify, resins having a Mw in excess of 30,000 tend to decline in resolution, though depending on a combination of monomers, and resins having a Mw in excess of 20,000 may have similar tendency. Resins having a Mw of less than 1,500 tend to have a rounded pattern profile, and resins having a Mw of less than 1,000 may have more tendency. During subsequent etching of the underlying film, such a rounded pattern profile can cause to prevent perpendicular etching of the film.

The second resist composition used in the double pattern forming process of the invention and comprising a polysiloxane compound as a base resin may further comprise an organic solvent, a compound capable of generating an acid in response to high-energy radiation (known as “acid generator”), and optionally, a dissolution inhibitor, a basic compound, a surfactant, and other components. These components including organic solvent, acid generator, dissolution inhibitor, basic compound, and surfactant are previously described in conjunction with the first resist composition and their examples are also the same as previously illustrated. Since the second resist material does not have the requirements of crosslinking reaction to acquire organic solvent resistance and positive elimination of acid labile groups for conversion to alkali solubility, addition of a thermal acid generator may be omitted. In the embodiment wherein the second resist composition used in the double pattern forming process comprises a polysiloxane compound as a base resin, a polysiloxane compound having a higher silicon content is desirable. Where other additives are organic compounds so that the overall resist composition may have a lower silicon content, it is preferred to reduce the amounts of organic compounds.

The resist material for forming a second resist pattern is preferably tailored such that a surface layer of the second resist film may have a higher rate of alkaline dissolution because reversal of the first resist pattern takes place smoothly. Enhancing the alkali solubility of only a surface layer of the pattern reversal film is advantageous for allowing for smooth dissolution of the pattern reversal film building up over the positive resist pattern which has been altered to be alkali soluble, and for enhancing the dimensional control of a trench pattern or hole pattern converted from the positive pattern. To enhance the surface alkali solubility, an alkali soluble surfactant, especially fluorochemical surfactant may be added. The preferred fluorochemical surfactants are those comprising either one or both of recurring units (s-1) and (s-2) represented by the general formula (4).

Herein, R^(s6) and R^(s9) are each independently hydrogen or methyl. The letter ns is equal to 1 or 2. In case of ns=1, X_(s1) is a phenylene group, —O—, —C(═O)—O—R^(s12)—, or —C(═O)—NH—R^(s12)— wherein R^(s12) is a single bond or a straight or branched C₁-C₄ alkylene group which may have an ester (—COO—) or ether (—O—) group. In case of ns=2, X_(s1) is a phenylene group with one hydrogen atom eliminated, or —C(═O)—O—R^(s81)═ or —C(═O)—NH—R^(s81)═ wherein R^(s81) is a straight, branched or cyclic C₁-C₁₀ alkylene group with one hydrogen atom eliminated, which may have an ester or ether group. R^(s7) is a single bond or a straight, branched or cyclic C₁-C₁₂ alkylene group. R^(s8) is hydrogen, fluorine, methyl, trifluoromethyl or difluoromethyl, or R^(s8) and R^(s7) may bond together to form a ring of 3 to 10 carbon atoms (exclusive of aromatic ring) with the carbon atom to which they are attached, which ring may have an ether group, fluorinated alkylene group or trifluoromethyl group. X_(s2) is a phenylene group, —O—, —C(═O)—O—R^(s11)—, or —C(═O)—N—-R^(s11)— wherein R^(s11) is a single bond or a straight or branched C₁-C₄ alkylene group which may have an ester or ether group. R^(s10) is a fluorine atom or a straight, branched or cyclic C₁-C₂₀ alkyl group, which may be substituted with at least one fluorine atom and which may have an ether, ester or sulfonamide group. The letter ms is an integer of 1 to 5 when X_(s2) is phenylene, and ms is 1 when X_(s2) is otherwise.

Examples of the monomers from which units (s-1) are derived include the above described examples of the monomers from which the recurring units substituted with acid labile groups of formula (AL-12)-20 are derived as well as the following.

Herein R^(s6) is as defined above.

Examples of the monomers from which recurring units (s-2) in formula (4) are derived are illustrated below while many recurring units (s-2) are units having a fluorinated alkyl group.

Herein R^(s9) is as defined above.

A total proportion of recurring units (s-1) and (s-2) is preferably 30 to 100 mol %, and more preferably 50 to 100 mol % of the fluorochemical surfactant.

These recurring units (s-1) and (s-2) may be copolymerized with the above-described alkali soluble recurring units having a phenol or carboxyl group or substantially alkali insoluble recurring units.

The alkali soluble surfactant is preferably added in an amount of 0 to 50 parts, and more preferably 0 to 20 parts by weight per 100 parts by weight of the base polymer. Too much amounts of the surfactant may cause excessive slimming or detract from etching resistance. When added, at least 1 phr of the surfactant is preferred.

Process

Now referring to the drawings, the double patterning process of the invention is illustrated. The first positive resist composition is coated on a substrate to form a first resist film thereon. As shown in FIG. 1, state (A), a first resist film 30 of a positive resist composition is formed on a processable substrate 20 disposed on a substrate 10 directly or via an intermediate intervening layer (not shown). The first resist film preferably has a thickness of 10 to 1,000 nm and more preferably 20 to 500 nm. Prior to exposure, the resist film is heated or prebaked, preferably at a temperature of 60 to 180° C., especially 70 to 150° C., even more preferably 80 to 120° C. for a time of 10 to 300 seconds, especially 15 to 200 seconds, even more preferably 30 to 120 seconds.

The substrate 10 used herein is generally a silicon substrate. The processable substrate 20 used herein includes SiO₂, SiN, SiON, SiOC, p-Si, α-Si, TiN, WSi, BPSG, SOG, Cr, CrO, CrON, MoSi, low dielectric constant film, and etch stopper film. The intermediate intervening layer includes hard masks of SiO₂, SiN, SiON or p-Si, an undercoat in the form of carbon film, a silicon-containing intermediate film, and an organic antireflective coating.

Preferably, a carbon film containing at least 75% by weight of carbon is disposed on the processable substrate, and a silicon-containing intermediate layer and a photoresist film are sequentially disposed thereon. Alternatively, a carbon film containing at least 75% by weight of carbon is disposed on the processable substrate, and a hard mask of SiO₂, SiN, SiON or p-Si, an organic antireflective coating (BARC), and a photoresist film are sequentially disposed thereon.

Where the second resist composition used in the double patterning process of the invention is a resist composition comprising a polysiloxane compound as defined above, the lower layer of the double pattern formed on the processable substrate is preferably made of an organic film-forming material so that the double pattern may be used as the so-called bilayer resist.

Where the double pattern is used as a bilayer resist, the organic film-forming material of which the lower layer of the double pattern formed on the processable substrate is made may be selected from many well-known materials. The organic film is briefly described. Basically, aromatic resins are preferred. More preferred are those resins which are crosslinked upon film formation so that intermixing may not occur when the resist composition is subsequently coated to form a film thereon.

Suitable aromatic resins include novolac resins and polyhydroxystyrene resins, and those resins having a fluorene or indene framework may be advantageously used in order to enhance the etch resistance of this organic film during etching of the substrate after pattern transfer to this organic film. Also an ARC may be formed on the organic film and a resist film according to the invention be formed thereon. The organic film having an antireflection function is preferred because the process becomes more simple. For such an antireflection function, it is preferred to use a resin having an anthracene or naphthalene framework or a benzene framework with conjugated unsaturated bond.

Crosslinks may be formed using thermosetting resins or a crosslinking technique employed in negative resist compositions. One common method uses a composition in solution form comprising a resin having functional groups such as phenol, alkoxyphenyl, alcohol or carboxylic acid, a substance capable of generating an acid through thermal decomposition, and a crosslinker (e.g., hexaalkoxymethylmelamine) capable of forming crosslinks with the functional groups in the presence of an acid catalyst. The composition is coated onto a processable substrate and heated to generate the acid whereby crosslinks are formed.

Then the first resist composition is exposed. For the exposure, preference is given to high-energy radiation having a wavelength of 140 to 250 nm, and especially ArF excimer laser radiation of 193 nm. The exposure may be done either in air or in a dry atmosphere with a nitrogen stream, or by immersion lithography in water. The ArF immersion lithography uses deionized water or liquids having a refractive index of at least 1 and highly transparent to the exposure wavelength such as alkanes as the immersion solvent. The immersion lithography involves prebaking a resist film and exposing the resist film to light through a projection lens, with water introduced between the resist film and the projection lens. Since this allows lenses to be designed to a NA of 1.0 or higher, formation of finer feature size patterns is possible. The immersion lithography is important for the ArF lithography to survive to the 45-nm node. In the case of immersion lithography, deionized water rinsing (or post-soaking) may be carried out after exposure for removing water droplets left on the resist film, or a protective film may be applied onto the resist film after pre-baking for preventing any leach-out from the resist film and improving water slip on the film surface. The resist protective film used in the immersion lithography is preferably formed from a solution of a polymer having 1,1,1,3,3,3-hexafluoro-2-propanol residues which is insoluble in water, but soluble in an alkaline developer liquid, in a solvent selected from alcohols of at least 4 carbon atoms, ethers of 8 to 12 carbon atoms, and mixtures thereof. After formation of the photoresist film, deionized water rinsing (or post-soaking) may be carried out for extracting the acid generator and the like from the film surface or washing away particles, or after exposure, rinsing (or post-soaking) may be carried out for removing water droplets left on the resist film.

Exposure is preferably carried out so as to provide an exposure dose of about 1 to 200 mJ/cm², more preferably about 10 to 100 mJ/cm², and even more preferably 10 to 50 mJ/cm². This is followed by baking on a hot plate at 60 to 150° C. for 30 seconds to 5 minutes, preferably at 80 to 120° C. for 30 seconds to 3 minutes (post-exposure baking =PEB).

Thereafter the first resist film is developed with a developer in the form of an aqueous alkaline solution, for example, an aqueous solution of 0.1 to 5 wt %, preferably 2 to 3 wt % tetramethylammonium hydroxide (TMAH) for 0.1 to 3 minutes, preferably 0.5 to 2 minutes by conventional techniques such as dip, puddle or spray techniques. In this way, a desired resist pattern 30 a is formed on the substrate as shown in FIG. 2, state (B).

The line pattern of the first resist film resulting from the above patterning process is removed, leaving a space pattern in a second resist film to which it is reversal transferred. When the space pattern to be reversal transferred to the second resist film is finished thin, such thin finish can be achieved by increasing the exposure dose of high-energy radiation applied in forming pattern 30 a of the first resist film. FIG. 3, state (B-1) shows an exemplary pattern having a line size reduced by over-exposure of the first resist film.

Next, the first resist pattern is treated so as to eliminate acid labile groups in the polymer and to crosslink the polymer, forming a crosslinked pattern 30 b as shown in FIG. 4, state (C). To induce elimination of acid labile groups and crosslinking to the polymer in the first resist pattern, acid and heat are necessary. In practice, an acid is generated, after which heat is applied to effect elimination of acid labile groups and crosslinking at the same time.

The acid may be generated by a suitable method such as flood exposure of the wafer (pattern) as developed for decomposing the photoacid generator. The flood exposure uses an exposure wavelength of 180 to 400 nm and an exposure dose of 10 mJ/cm² to 1 J/cm². Radiation with a wavelength of less than 180 nm, specifically irradiation of excimer lasers of 172 nm, 146 nm and 122 nm or excimer lamps is undesirable because not only the generation of acid from photoacid generator, but also photo-induced crosslinking reaction are accelerated, leading to a decrease of alkaline dissolution rate due to excessive crosslinking. For the flood exposure, use is preferably made of an ArF excimer laser with a wavelength longer than 193 nm, a KrCl excimer lamp of 222 nm, a KrF excimer laser of 248 nm, a low-pressure mercury lamp centering at 254 nm, a XeCl excimer lamp of 308 nm, and i-line of 365 nm.

However, it is desired to avoid the use of an equipment for flood exposure because the equipment itself is expensive and because of the disadvantage that if it is built in the semiconductor device production line, the throughput of the line is reduced by an increased number of steps.

As mentioned above, in the step of treating the first resist pattern to eliminate acid labile groups in the polymer and to crosslink the polymer to form a crosslinked pattern 30 b as shown in FIG. 4, state (C), acid and heat are necessary for elimination and crosslinking. To positively generate an acid, a thermal acid generator may be added to the first resist composition.

In the embodiment wherein a thermal acid generator in the form of an ammonium salt is added to the positive resist composition, an acid can be generated by heating. In this embodiment, acid generation and crosslinking reaction take place simultaneously. Preferred heating conditions include a temperature of 180 to 220° C. and a time of 10 to 300 seconds, especially 30 to 60 seconds. As a result, a crosslinked resist pattern which is insoluble in the solvent of the second resist composition or reversal film-forming composition is yielded.

Suitable ammonium salts serving as the thermal acid generator include compounds of the formula (P1a-2). The addition of a thermal acid generator to the first resist composition is advantageous in that it helps the first resist film to exhibit alkali solubility and it promotes crosslinking reaction to impart resistance to the organic solvent used in coating of a second resist film. However, excess addition of a thermal acid generator gives rise to some problems. The thermal acid generator may be added in such amounts as to provide no impact on the lithography of patterning the first resist film, no impact on the thermal properties of the first resist film, and no impact on the second resist film. Specifically, the thermal acid generator may be added in an amount of up to 5%, preferably up to 3%, and more preferably 0.01 to 1% by weight based on the weight of the base resin in the first resist film.

Herein K⁻ is a sulfonate having at least one fluorine substituted at α-position, or perfluoroalkylimidate or perfluoroalkylmethidate. R^(101d), R^(101e), R^(101f), and R^(101g) are each independently hydrogen, a straight, branched or cyclic alkyl, alkenyl, oxoalkyl or oxoalkenyl group of 1 to 12 carbon atoms, an aryl group of 6 to 20 carbon atoms, or an aralkyl or aryloxoalkyl group of 7 to 12 carbon atoms, in which some or all hydrogen atoms may be substituted by alkoxy groups. Alternatively, R^(101d) and R^(101e), or R^(101d), R^(101e) and R^(101f) may bond together to form a ring with the nitrogen atom to which they are attached, and each of R^(101e) and R^(101f) or each of R^(101d), R^(101e) and R^(101f) is a C₃-C₁₀ alkylene group or a hetero-aromatic ring having incorporated therein the nitrogen atom when they form a ring.

Examples of K⁻ include perfluoroalkanesulfonates such as triflate and nonaflate, imidates such as bis(trifluoromethylsulfonyl)imide, bis(perfluoroethylsulfonyl)imide, and bis(perfluorobutylsulfonyl)imide, methidates such as tris(trifluoromethylsulfonyl)methide and tris(perfluoroethylsulfonyl)methide, and sulfonates having fluorine substituted at α-position, represented by the formula (K-1), and sulfonates having fluorine substituted at α-position, represented by the formula (K-2).

In formula (K-1), R^(102a) is hydrogen, a straight, branched or cyclic C₁-C₂₀ alkyl or acyl group, C₂-C₂₀ alkenyl group or C₆-C₂₀ aryl or aryloxy group, which may have an ether, ester, carbonyl group or lactone ring and in which some or all hydrogen atoms may be substituted by fluorine atoms. In formula (K-2), R^(102b) is hydrogen, a straight, branched or cyclic C₁-C₂₀ alkyl group, C₂-C₂₀ alkenyl group or C₆-C₂₀ aryl group.

Apart from the embodiment of performing flood exposure and the embodiment of adding a thermal acid generator to positively generate an acid in the first resist pattern, there is a possible embodiment wherein a minor amount of residual acid which has diffused from the exposed area and remains in the first resist pattern react with acid labile groups at elevated temperature whereby the acid labile groups are eliminated so that the first positive resist pattern turns to be alkali soluble, and crosslinking reaction take place under the action of that acid and heat so that the pattern is endowed with solvent resistance. It has been observed that some acid labile groups are thermally eliminated by heating at high temperature. It has also been observed that the first resist pattern is converted from a positive behavior to be insoluble in alkaline developer to an alkaline developer soluble behavior by heating at high temperature. As long as the first resist composition according to the invention is used, acid-assisted elimination of acid labile groups for the first resist pattern to convert from alkaline developer insolubility to solubility and impartment of resistance to organic solvent in the second resist composition for reversal transfer can be accomplished simply by heating at high temperature. In the step of heating at high temperature to facilitate conversion of the first resist film to be alkali soluble and crosslinking reaction to impart resistance to organic solvent used in coating of the second resist film, an appropriate temperature is at least 150° C., and more preferably in the range of 180 to 220° C. In general, a photoacid generator and basic compound in a resist composition serve as plasticizers, with the tendency that the resist pattern has a lower Tg and thermal flow begins at a lower temperature. Since the photoacid generator and basic compound are essential for the resist composition, it is necessary to select a base resin having a high Tg while taking into account the plasticizing effect by the addition of photoacid generator and basic compound. An appropriate Tg of base resin is at least 150° C., and more preferably at least 180° C. If the temperature reached by heating to induce crosslinking reaction is higher than 220° C., then an optimum first resist pattern for reversal transfer to the second resist cannot be obtained due to substantial thermal shrinkage or thermal damage to the first resist pattern. If the temperature reached by heating to induce crosslinking reaction is lower than 150° C., then crosslinking reaction may occur short.

Next, as shown in FIG. 5, state (D), the reversal film-forming composition or second resist composition is coated and built up until it covers or overlies the crosslinked first resist pattern 30 b, forming a reversal film (or second resist film) 40.

In another embodiment, the first resist pattern has an increased height, and the coating of the second resist film has a reduced thickness as shown in FIG. 6, state (D-1). Then the first resist pattern which has been converted to be soluble in alkaline developer may be exposed to an alkaline developer whereby the first resist pattern may be removed from the second resist film serving as the reversal transfer film.

In the embodiment shown in FIG. 5, state (D), the second resist film (serving as the reversal transfer film) overlying the first resist pattern must be removed so that the first resist pattern which has been converted (or reversed) to be soluble in alkaline developer may be contacted with an alkaline developer. Then the second resist film (serving as the reversal transfer film) overlying the first resist pattern is previously converted to be somewhat soluble in alkaline developer and then slimmed until the first resist pattern which has been converted to be soluble in alkaline developer is exposed to an alkaline developer.

Where the second resist film (serving as the reversal transfer film) overlying the first resist pattern is removed until access is gained to the first resist pattern which has been converted to be soluble in alkaline developer, this may be accomplished by a measure other than the above-mentioned measure of endowing the second resist film (serving as the reversal transfer film) with solubility in alkaline developer. The alternative measure is as follows. In the step of heating at high temperature to endow the first resist pattern with resistance to solvent used in coating of the second resist film while keeping some acid which has diffused from the exposed area and remains in the first resist pattern or keeping the first resist pattern soluble in alkaline developer, the photoacid generator remaining in the first resist pattern from the resist composition is thermally decomposed to generate an acid which acts on alkali soluble groups protected with acid labile groups which are eliminatable with acid in the second resist film overlying the first resist pattern. Then, acid elimination occurs in the baking steps involved in a process comprising the steps of coating, prebaking, exposing and post-exposure baking the second resist film, whereby the second resist film overlying the first resist pattern is converted to be alkali soluble. As a result, during development of the second resist film for patterning, the second resist film overlying the first resist pattern can also be dissolved away, and the reversed first resist pattern can be removed.

In the embodiment wherein the second resist film (serving as reversal transfer film) overlying the reversed first resist pattern is removed solely by heating at high temperature so that the first resist pattern may be dissolved in an alkaline developer, the coating thicknesses of first and second resist films become crucial. Appropriate thicknesses of first and second resist films to be coated are discussed below. Relative to the thickness of a first resist film coated onto a flat substrate, the thickness of a second resist film coated onto a flat substrate is preferably 60 to 50%. If the coating thickness of a second resist film is thicker than the range, the second resist film overlying the first resist pattern may not be fully converted to be alkali soluble, the second resist film may not be removed, an alkaline developer may not gain access to the first resist pattern, and reversal and removal of the first resist pattern may not be done. If the coating thicknesses are too thin, a double pattern obtained after patterning of the second resist including a pattern of reversal transfer of the first resist pattern may not have a certain thickness.

FIG. 7 shows the state (E) that the reversed first resist pattern is dissolved away in an alkaline developer without patterning of the second resist film serving as the reversal transfer film.

On the other hand, the first resist pattern which has been converted to be soluble in alkaline developer ensures that reversal of the first resist pattern and pattern formation of the second resist film take place simultaneously during the development step for patterning the second resist film.

The second resist film for reversal transfer coated on the first resist pattern is patterned by the same method as the first resist film patterning method. The method is the same as described for the patterning of the first resist film.

Notably, the patterning of the second resist film may be performed by several modes which have their own advantage.

One mode is by effecting exposure to form a second resist pattern so that spaces thereof (exposed area 50) are disposed between features of the reversed first resist pattern as shown in FIG. 8, state (F-1). In this case, the first resist pattern converted to be alkali soluble is dissolved away in an alkaline developer to leave spaces, and the second resist pattern defines spaces therebetween. As a result, a double patterning process of forming closely packed lines and spaces becomes possible, FIG. 9, state (F-2).

Advantageously this double patterning process of forming a closely packed line-and-space pattern has an ability to form lines and spaces of a size which cannot be achieved by the single patterning process.

Another mode of exposure of the second resist film is by effecting exposure at a position spaced apart from the first resist pattern to be reversed into spaces as shown in FIG. 10, state (F-3).

In state (F-3) of FIG. 10, the first resist pattern is finished as thin lines as a result of over-exposure, and converted to be alkali soluble by heating at high temperature, whereby the pattern is finished as thin (or narrow) spaces. A patterning process of forming a very thin space pattern and an isolated line pattern at the same time is very difficult because their characteristics are in trade-off relationship. The double patterning process of the invention succeeds in overcoming the trade-off because a very thin space pattern can be formed by reversal transfer of the first resist film and an isolated line pattern can be formed by patterning the second resist film. The process is advantageous in processing a layer to form fine spaces and isolated lines in combination as shown in FIG. 11, state (F-4).

A further mode is exposure of the second resist film to a cutout pattern transverse to the first resist pattern as shown in FIG. 12, step (G-1). By developing the exposed area 50 of the second resist film and the positive/negative reversed first resist pattern, a crisscross cutout pattern intersecting the second pattern in the form of trench pattern can be formed as shown in FIG. 13, state (G-2).

A still further mode is exposure of the second resist film to a remain line pattern perpendicular to the first resist pattern as shown in FIG. 14, state (H-1). Since the second lines are interrupted by the first pattern, a pattern of rectangular shaped dots at a fine pitch can be formed as shown in FIG. 15, state (H-2). This method results in rectangular holes, although a double dipole method generally forms a dot pattern consisting of circular shaped holes as shown in FIG. 17.

A still further mode involves double exposures of lines in X and Y directions as shown in FIG. 16, state (I-1), and subsequent development to form a dot pattern as shown in FIG. 17, state (I-2). A second resist composition is coated thereon, exposed to a pattern of holes disposed between the dots, and developed. Development of the thus exposed second resist film facilitates positive/negative reversal of the first pattern from the dot pattern to a hole pattern, which is resolved at the same time as holes of the second pattern as shown in FIG. 18, state (I-3). In FIG. 16, 30 c is an exposed area resist pattern.

For exposure of the second resist, high-energy radiation having a wavelength of up to 300 nm is preferably used. Examples of such radiation include a KrF excimer laser with a wavelength of 248 nm, an ArF excimer laser of 193 nm, a F₂ laser of 157 nm, EB, EUV, and x-ray. Of these, the ArF excimer laser of 193 nm is preferably used. The exposure from the ArF excimer laser may be either immersion lithography using water or dry lithography, with the immersion lithography being preferred for forming finer size patterns. In the ArF excimer laser lithography, materials having aromatic rings (exclusive of naphthalene rings) cannot be used as the base polymer, and instead, methacrylates and other materials having a cyclic structure are preferably used. Where KrF excimer laser, EB or EUV lithography is applied, materials having aromatic rings like phenol groups may be used.

When it is desired to form fine holes between features of the first resist pattern using the second resist serving as image reversal film, as shown in FIGS. 16 to 18, the use of ArF excimer laser or EB lithography is preferred because a very high resolution capability is required.

Furthermore, using the reversed pattern 40 a as a mask, the intermediate intervening layer of hard mask or the like (if any) may be etched, and the processable substrate 20 further etched. For etching of the intermediate intervening layer of hard mask or the like, dry etching with fluorocarbon or halogen gases may be used. For etching of the processable substrate, the etching gas and conditions may be properly chosen so as to establish an etching selectivity relative to the hard mask, and specifically, dry etching with fluorocarbon, halogen, oxygen, hydrogen or similar gases may be used. Thereafter, the crosslinked resist film and second resist film are removed. Removal of these films may be carried out after etching of the intermediate intervening layer of hard mask or the like. It is noted that removal of the crosslinked resist film may be achieved by dry etching with oxygen or radicals and removal of the second resist film may be achieved as previously described, or using strippers such as amines, sulfuric acid/aqueous hydrogen peroxide or organic solvents.

EXAMPLE

Examples of the invention are given below by way of illustration and not by way of limitation. The abbreviations used herein are GPC for gel permeation chromatography, Mw for weight average molecular weight, Mn for number average molecular weight, Mw/Mn for molecular weight distribution or dispersity, NMR for nuclear magnetic resonance, PAG for photoacid generator, TAG for thermal acid generator, Me for methyl, and Et for ethyl. For all polymers, Mw and Mn are determined by GPC versus polystyrene standards.

Synthesis Example 1

Polymers for use in first resist compositions for reversal and second resist compositions subject to reversal transfer of first resist film were prepared by combining various monomers, effecting copolymerization reaction in tetrahydrofuran medium, crystallization in methanol, repeatedly washing with hexane, isolation, and drying. The resulting polymers (Resist Polymers 1 to 9 and Comparative Resist Polymers 10 to 12) had the composition shown below. Notably, a phenol group on a monomer was substituted by an acetoxy group, which was converted back to a phenol group by alkaline hydrolysis after polymerization. The composition of each polymer was analyzed by ¹H-NMR, and the Mw and Mw/Mn determined by GPC.

Resist Polymer 1

(polymer for use in first resist composition)

-   -   Mw=8,300     -   Mw/Mn=1.73

Resist Polymer 2

(polymer for use in first resist composition)

-   -   Mw=7,300     -   Mw/Mn=1.67

Resist Polymer 3

(polymer for use in first and second resist compositions)

-   -   Mw=7,700     -   Mw/Mn=1.68

Resist Polymer 4

(polymer for use in first resist composition)

-   -   Mw=7,500     -   Mw/Mn=1.67

Resist Polymer 5

(polymer for use in first resist composition)

-   -   Mw=8,000     -   Mw/Mn=1.71

Resist Polymer 6

(polymer for use in first resist composition)

-   -   Mw=6,700     -   Mw/Mn=1.67

Resist Polymer 7

(polymer for use in first resist composition)

-   -   Mw=7,800     -   Mw/Mn=1.66

Resist Polymer 8

(polymer for use in second resist composition)

-   -   Mw=7,900     -   Mw/Mn=1.67

Resist Polymer 9

(polymer for use in second resist composition)

-   -   Mw=7,400     -   Mw/Mn=1.63

Comparative Resist Polymer 10

(comparative polymer for use in first resist composition)

-   -   Mw=7,700     -   Mw/Mn=1.68

Comparative Resist Polymer 11

(comparative polymer for use in first resist composition)

-   -   Mw=6,600     -   Mw/Mn=1.67

Comparative Resist Polymer 12

(comparative polymer for use in first resist composition)

-   -   Mw=7,500     -   Mw/Mn=1.80

Polysiloxanes for use in second resist compositions for reversal transfer were synthesized as follows.

Synthesis Example 2

A 200-ml four-neck flask equipped with a stirrer, reflux condenser, dropping funnel, and thermometer was charged with 0.2 g of acetic acid, 20 g of water and 20 g of ethanol and kept at 30° C. To the flask, a solution of 10.8 g (30 mmol) of triethoxysilane compound A, 8.8 g (20 mmol) of triethoxysilane compound B, and 16.4 g (50 mmol) of triethoxysilane compound C in 40 g of ethanol was added dropwise over 3 hours.

The reaction mixture was aged at 30° C. for a further 20 hours, diluted with methyl isobutyl ketone, repeatedly washed with water until the organic layer became neutral, and concentrated, yielding 27.6 g of an oligomer.

Using 50 g of toluene, the oligomer was transferred into a 100-ml three-neck flask equipped with a stirrer, reflux condenser, and thermometer. Then 56 mg of potassium hydroxide was added to the solution, which was heated under reflux for 20 hours. The reaction solution was cooled, diluted with methyl isobutyl ketone, repeatedly washed with water until the organic layer became neutral, and concentrated, yielding 24.9 g of a polymer.

On NMR and GPC analysis, the product was identified to be Resist Polymer 13 of the following compositional formula, having a Mw of 3,500.

Resist Polymer 13

(polysiloxane for use in second resist composition)

-   -   Mw=3,500

Variants of the ethoxysilane compound of the structure shown above could be formed by changing the silicon-bonded substituent structure. Thereafter, using these ethoxysilane variants, polysiloxane compounds of different constituent units, designated Resist Polymers 14 and 15, were synthesized by the same procedure as the above synthesis example.

Resist Polymer 14

(polysiloxane for use in second resist composition)

-   -   Mw=3,600

Resist Polymer 15

(polysiloxane for use in second resist composition)

-   -   Mw=2,000

Resist Polymer 16

(phenolic polymer for use in second resist composition)

-   -   Mw=6,000

Resist Polymer 17

(phenolic polymer for use in second resist composition)

-   -   Mw=7,400

Resist Polymer 18

(phenolic polymer for use in second resist composition)

-   -   Mw=6,300

Resist Polymer 19

(phenolic polymer for use in second resist composition)

-   -   Mw=6,600

Resist Polymer 20

(phenolic polymer for use in second resist composition)

-   -   Mw=6,600

EXAMPLE AND COMPARATIVE EXAMPLE

The polymers synthesized above were combined with a photoacid generator, basic compound, surfactant, thermal acid generator, surface dissolution rate improver (Surface DRR), and organic solvent. To 100 parts of the organic solvent was added 0.005 parts of surfactant FC-4430 (Sumitomo 3M Co., Ltd.). The ingredients were thoroughly mixed to form resist compositions.

-   Acid generator: PAG1, 2 of the following structural formula

-   Basic compound: Quencher 1 to 3 of the following structural formula

Thermal Acid Generator:

TAG1 of the following structural formula

Surface Dissolution Rate Improver:

Surface DRR of the following structural formula

Organic Solvent: Propylene Glycol Monomethyl Ether Acetate (PGMEA)

Table 1 tabulates the formulation of first resist composition, second resist composition and comparative first resist composition.

TABLE 1 Resist Formulation Polymer PAG Basic compound TAG Solvent composition No. (pbw) (pbw) (pbw) (pbw) (pbw) 1st resist I-001 Resist Polymer 1 PAG1 Quencher 1 — PGMEA (100) (16) (3) (2,700) 1st resist I-002 Resist Polymer 2 PAG1 Quencher 1 — PGMEA (100) (16) (3) (2,700) 1st resist I-003 Resist Polymer 3 PAG1 Quencher 1 — PGMEA (100) (16) (3) (2,700) 1st resist I-004 Resist Polymer 4 PAG1 Quencher 1 — PGMEA (100) (16) (3) (2,700) 1st resist I-005 Resist Polymer 4 PAG1 Quencher 1 TAG1 PGMEA (100) (16) (3) (0.5) (2,700) 1st resist I-006 Resist Polymer 5 PAG1 Quencher 1 — PGMEA (100) (16) (3) (2,700) 1st resist I-007 Resist Polymer 6 PAG1 Quencher 1 — PGMEA (100) (16) (3) (2,700) 1st resist I-008 Resist Polymer 7 PAG1 Quencher 1 — PGMEA (100) (16) (3) (2,700) Comparative I-009 Resist Polymer 10 PAG1 Quencher 1 — PGMEA 1st resist (100) (16) (3) (2,700) Comparative I-010 Resist Polymer 11 PAG1 Quencher 1 — PGMEA 1st resist (100) (16) (3) (2,700) Comparative I-011 Resist Polymer 12 PAG1 Quencher 1 — PGMEA 1st resist (100) (16) (3) (2,700) 2nd resist II-001 Resist Polymer 3 PAG1 Quencher 1 — PGMEA (100) (16) (7) (5,000) 2nd resist II-002 Resist Polymer 8 PAG1 Quencher 1 — PGMEA (100) (16) (7) (5,000) 2nd resist II-003 Resist Polymer 9 PAG1 Quencher 1 — PGMEA  (93) (16) (7) (5,000) Surface DRR  (7) 2nd resist II-004 Resist Polymer 13 PAG1 Quencher 2 — PGMEA (100)  (6) (1) (3,500) 2nd resist II-005 Resist Polymer 14 PAG1 Quencher 2 — PGMEA (100)  (6) (1) (3,500) 2nd resist II-006 Resist Polymer 15 PAG1 Quencher 2 — PGMEA (100)  (6) (1) (3,500) 2nd resist II-007 Resist Polymer 16 PAG2 Quencher 3 — PGMEA (100)  (8)   (1.5) (3,500) 2nd resist II-008 Resist Polymer 17 PAG2 Quencher 3 — PGMEA (100)  (8)   (1.5) (3,500) 2nd resist II-009 Resist Polymer 18 PAG2 Quencher 3 — PGMEA (100)  (8)   (1.5) (3,500) 2nd resist II-010 Resist Polymer 19 PAG2 Quencher 3 — PGMEA (100)  (8)   (1.5) (3,500) 2nd resist II-011 Resist Polymer 20 PAG2 Quencher 3 — PGMEA (100)  (8)   (1.5) (3,500)

Table 2 tabulates the first resist patterning data of Examples 1 to 8 and Comparative Examples 1 to 3.

The resist compositions prepared according to the formulation shown in Table 1 were filtered through a tetrafluoroethylene filter having a pore size of 0.2 μm, yielding positive resist film-forming coating solutions.

On a substrate (silicon wafer) having deposited thereon an antireflective coating (ARC-29A, Nissan Chemical Industries, Ltd.) of 90 nm thick, each of the resist compositions was spin coated and prebaked on a hot plate at an optimum temperature for 60 seconds to form a resist film of 1,200 Å thick. As used herein, the term “optimum temperature” refers to the prebaking temperature which ensures that a pattern resulting from subsequent processing has a satisfactory profile which is highly rectangular and free of bridges or pattern edge chipping, when observed under top-down scanning electron microscope (TDSEM) S9320 (Hitachi, Ltd.). The optimum prebaking temperature is shown in Table 2.

The first resist film thus formed was subjected to pattern exposure by means of an ArF excimer laser scanner S-307E (Nikon Corp., NA 0.85, σ 0.93-0.62, dipole illumination). The mask used was a 6% halftone phase shift mask (HTPSM) bearing thereon a line-and-space design consisting of 70-nm lines and 160-nm pitches (equivalent resist pattern size). Exposure of the resist film was done while selecting an optimum focus and varying the exposure dose from a minimum dose to a maximum dose.

Following exposure, the resist film was baked on a hot plate (post-exposure bake, PEB). The appropriate PEB temperature for each resist composition is also reported in Table 2. The appropriate PEB temperature refers to the temperature at which a wide process margin is observed for that resist composition. PEB for 60 seconds was followed by development in a 2.38 wt % tetramethylammonium hydroxide (TMAH) aqueous solution for 30 seconds, yielding a positive pattern.

Table 2 reports the optimum exposure dose at which 40-nm lines were finished from the line-and-space design consisting of 70-nm lines and 160-nm pitches (equivalent resist pattern size) on the mask.

Now, to convert the first resist film to be alkali soluble and to impart thereto resistance to solvent for a second resist film to which the first resist pattern is to be transferred, the first resist film was heated at a high temperature. This heating was done on a hot plate at a temperature of 200° C. for 60 seconds. After this heating, a change in the size of 40-nm lines finished as above was measured. Table 2 reports the line size after heating.

TABLE 2 Optimum exposure dose capable of 40 nm finish from Line size 1st mask design of after resist Prebaking PEB 70 nm line/ 200° C. × 60 sec formulation temperature temperature 160 nm pitch heating No. (° C. × 60 sec) (° C. × 60 sec) (mJ) (nm) Example 1 I-001 100 100 50 37 Example 2 I-002 100 90 52 39 Example 3 I-003 100 90 52 38 Example 4 I-004 115 110 47 38 Example 5 I-005 115 110 43 39 Example 6 I-006 105 95 53 38 Example 7 I-007 100 100 45 38 Example 8 I-008 100 100 45 37 Comparative I-009 100 100 50 45 Example 1 Comparative I-010 100 100 50 43 Example 2 Comparative I-011 95 90 50 52 Example 3

In Comparative Example 3, the 40 nm lines after patterning were changed to be thicker by 200° C.×60 sec heating. A thermal flow was observed in the first resist pattern of Comparative Example 3 because the resist composition had a low glass transition temperature (Tg). The resist composition of Comparative Example 3 is inadequate because of a failure of nano-scale patterning of the first resist as reversal transfer pattern.

Next, a second resist composition was coated onto the first resist pattern obtained in Examples 1 to 8 and Comparative Examples 1 and 2. The coating thickness of the second resist composition was set at 600 Å on a flat substrate. Table 3 shows a change of the first resist pattern when the second resist composition was coated thereon. The prebaking temperature in coating of the second resist composition is also reported in Table 3.

TABLE 3 2nd resist coating 2nd resist thickness 2nd resist prebaking on flat 1st resist pattern 1st resist formulation temperature substrate after pattern No. (° C. × 60 sec) (Å) 2nd resist coating Example 9 pattern of II-001 100 600 2nd resist was properly Example 1 coated on 1st resist Example 10 pattern of II-001 100 600 2nd resist was properly Example 2 coated on 1st resist Example 11 pattern of II-001 100 600 2nd resist was properly Example 3 coated on 1st resist Example 12 pattern of II-001 100 600 2nd resist was properly Example 4 coated on 1st resist Example 13 pattern of II-001 100 600 2nd resist was properly Example 5 coated on 1st resist Example 14 pattern of II-001 100 600 2nd resist was properly Example 6 coated on 1st resist Example 15 pattern of II-001 100 600 2nd resist was properly Example 7 coated on 1st resist Example 16 pattern of II-001 100 600 2nd resist was properly Example 8 coated on 1st resist Comparative pattern of II-001 100 600 1st resist was dissolved Example 4 Comparative in 2nd resist solution, Example 1 pattern was disrupted Comparative pattern of II-001 100 600 1st resist was dissolved Example 5 Comparative in 2nd resist solution, Example 2 pattern was disrupted

In Comparative Examples 4 and 5, the first resist pattern was disrupted by attack of the solvent in the second resist composition. Since the polymers in the first resist compositions of Comparative Examples 4 and 5 were not crosslinked during the high-temperature heating step for imparting organic solvent resistance, they were dissolved in the second resist solvent.

Next, a second resist composition was coated onto the first resist pattern obtained in Examples 1 to 8 as above. The second resist film thus coated was directly (without pattern exposure) baked (PEB) at a temperature for the second resist film and then developed with a 2.38 wt % TMAH solution for 30 seconds. Since the first resist pattern had been converted alkali soluble, its pattern was reversal transferred to the second resist film. This was observed under TDSEM S9320 (Hitachi, Ltd.). In addition the size of the pattern which was reversal transferred to the second resist film was measured. The results are shown in Table 4.

In a comparative example, coatings of the second resist composition having varying thickness were formed and the patterns of the second resist film after reversal transfer were observed. The results are shown in Table 4. If the second resist film is thick, the alkaline developer may not readily gain access to the first resist film which has been converted to be alkali soluble, causing transfer failure.

TABLE 4 2nd resist Pattern (space) Pattern (space) 2nd coating 2nd reversal reversal 2nd resist thickness resist transferred to transferred to 1st resist prebaking on flat PEB 2nd resist 2nd resist resist formulation temperature substrate temperature film, film, pattern No. (° C. × 60 sec) (Å) (° C. × 60 sec) TDSEM profile size (nm) Example 17 pattern of II-001 100 600 90 good 30 Example 1 Example 18 pattern of II-001 100 600 90 good 32 Example 2 Example 19 pattern of II-001 100 600 90 good 31 Example 3 Example 20 pattern of II-001 100 600 90 good 33 Example 4 Example 21 pattern of II-001 100 600 90 good 33 Example 5 Example 22 pattern of II-001 100 600 90 good 35 Example 6 Example 23 pattern of II-001 100 600 90 good 32 Example 7 Example 24 pattern of II-001 100 600 90 good 36 Example 8 Example 25 pattern of II-002 100 600 100 good 33 Example 4 Example 26 pattern of II-003 100 600 100 good 31 Example 4 Example 27 pattern of II-004 120 600 100 good 30 Example 4 Example 28 pattern of II-005 120 600 100 good 32 Example 4 Example 29 pattern of II-006 120 600 100 good 33 Example 4 Comparative pattern of II-001 120 700 100 bridges in — Example 6 Example 4 spaces of reversal transferred pattern, spaces not fully open Comparative pattern of II-001 120 800 100 spaces almost — Example 7 Example 4 closed Comparative pattern of II-001 120 900 100 even trace of — Example 8 Example 4 reversal pattern not observed

Next, on the first resist pattern which had been converted (or reversed) to be soluble in alkaline developer, a second resist film was formed and exposed under the following conditions so as to define a pattern of spaces between features of the first resist pattern. Pattern exposure was carried out by means of an ArF scanner S-307E (Nikon Corp., NA 0.85, σ 0.93-0.62, dipole illumination). The mask used was a 6% halftone phase shift mask (HTPSM) bearing thereon a line-and-space design consisting of 70-nm lines and 160-nm pitches (equivalent resist pattern size). Exposure of the second resist film was done while selecting an optimum focus and varying the exposure dose from a minimum dose to a maximum dose. The same mask as used in exposure of the first resist film was used at this stage, because the line pattern in the unexposed area of the first resist was reversed into a space pattern and its position overlapped the line pattern in the unexposed area of second resist pattern exposure, and so the same line-and-space arrangement might be used. Since the mask bears thereon a line-and-space design consisting of 70-nm lines and 160-nm pitches (or 90-nm spaces), a second resist space pattern of 40 nm could be resolved at a low exposure dose. The space pattern size resulting from reversal transfer of the first resist was intended to be 40 nm. This succeeded in a double patterning process capable of forming repeat patterns of 40-nm lines (and spaces) and 80-nm pitches. The results are shown in Table 5. Table 5 also reports the exposure dose of resolving the second resist to 40 nm and the profile following double patterning.

TABLE 5 Optimum exposure for space 2nd 40 nm finish resist from 2nd coating 2nd 2nd resist 2nd resist thickness resist mask design Profile 1st resist prebaking on flat PEB of after resist formulation temperature substrate temperature 70 nm line/ double pattern No. (° C. × 60 sec) (Å) (° C. × 60 sec) 160 nm pitch patterning Example 30 pattern of II-001 100 600 90 32 some top loss Example 1 Example 31 pattern of II-001 100 600 90 32 some top loss Example 2 Example 32 pattern of II-001 100 600 90 32 some top loss Example 3 Example 33 pattern of II-001 100 600 90 32 some top loss Example 4 Example 34 pattern of II-001 100 600 90 32 some top loss Example 5 Example 35 pattern of II-001 100 600 90 32 some top loss Example 6 Example 36 pattern of II-001 100 600 90 32 some top loss Example 7 Example 37 pattern of II-001 100 600 90 32 some top loss Example 8 Example 38 pattern of II-002 100 600 100 32 rounded Example 4 Example 39 pattern of II-003 100 600 100 30 rectangular, Example 4 good Example 40 pattern of II-004 120 600 100 30 some top loss Example 4 Example 41 pattern of II-005 120 600 100 28 rectangular, Example 4 good Example 42 pattern of II-006 120 600 100 28 rectangular, Example 4 good

On a silicon wafer, an undercoat material ODL-50 (Shin-Etsu Chemical Co., Ltd.) was coated and baked on a hot plate at 250° C. for 60 seconds to form an undercoat of 200 nm thick (carbon content 80 wt %). A silicon-containing intermediate film material SHB-A940 (Shin-Etsu Chemical Co., Ltd.) was coated thereon and baked at 200° C. for 60 seconds to form a silicon-containing intermediate film of 35 nm thick (silicon content 43 wt %). A photoresist composition was coated thereon and prebaked at 100° C. for 60 seconds to form a first photoresist film of 120 nm thick.

The first resist film thus formed was exposed to a pattern of five Y direction lines having a width of 70 nm, a pitch of 140 nm and a length of 700 nm by means of an ArF excimer laser scanner S-307E (Nikon Corp., NA 0.85, σ 0.93-0.62, dipole illumination for Y-direction lines) through a 6% halftone phase shift mask. Following exposure, the film was baked (PEB) at 100° C. for 60 seconds and developed with a 2.38 wt % TMAH solution for 30 seconds. A pattern of 70 nm lines in Y direction was formed and then baked at 190° C. for 60 seconds to induce crosslinking and deprotection. The line width of the first resist pattern was measured.

In Example 43, a second resist composition was coated on the first line pattern to form a second resist film of 50 nm thick. To define a single X-direction line intersecting perpendicularly the first pattern, the second resist film was exposed to a trench pattern having a line width of 150 nm and a length of 1 μm by means of an ArF excimer laser scanner S-307E (Nikon Corp., NA 0.85, σ 0.93-0.62, annular illumination) through a 6% halftone phase shift mask. This was followed by baking at 100° C. for 60 seconds and development in a 2.38 wt % TMAH solution for 30 seconds, yielding a X-direction trench pattern having a width of 150 nm intersecting the five Y-direction 70 nm trenches.

In Example 44, a second resist composition was coated on the first line pattern to form a second resist film of 60 nm thick. To define a single X-direction line intersecting perpendicularly the first pattern, the second resist film was exposed to a trench pattern having a line width of 200 nm and a length of 1 μm by means of a KrF excimer laser scanner S-203B (Nikon Corp., NA 0.68, σ 0.75-0.50, annular illumination) through a 6% halftone phase shift mask. This was followed by baking at 100° C. for 60 seconds and development in a 2.38 wt % TMAH solution for 30 seconds, yielding a X-direction trench pattern having a width of 200 nm intersecting the five Y-direction 70 nm trenches.

In Comparative Example 9, the resist film was exposed by means of an ArF excimer laser scanner S-307E (Nikon Corp., NA 0.85, σ 0.93-0.62, cross-pole illumination) through a 6% halftone phase shift mask having a 150 nm X-direction trench pattern (calculated as on-wafer size) overlapping a pattern of five Y-direction 70 nm lines at 140 nm pitches, as shown in FIG. 19 (consisting of a shifter light-shielding region in grey zone G and a light-transmissive region in white zone W). This was followed by baking at 100° C. for 60 seconds and development in a 2.38 wt % TMAH solution for 30 seconds, yielding a 150 nm wide X-direction trench pattern intersecting the five Y-direction 70 nm trenches.

The size of the line pattern of first resist Y-direction lines and the space width measurement size of Y-direction spaces after second resist development and subsequent reversal, the size of X-direction trenches of second resist pattern, and the profile at the intersection between the second pattern and the first pattern were observed under SEM. The results are shown in Table 6.

FIG. 19 shows the resist pattern obtained in Examples 43 and 44, and FIG. 20 shows the resist pattern obtained in Comparative Example 9. The grey zone G designates the region where the resist is retained, and the white zone W designates the region where the resist has been dissolved away.

TABLE 6 1st resist 1st 2nd pattern Shape of 1st 2nd resist resist size intersection resist resist pattern pattern after between formulation formulation size size reversal 1st and 2nd No. No. (nm) (nm) (nm) patterns Example 43 I-001 II-001 70 150 72 perpendicular Example 44 I-001 II-007 70 200 73 perpendicular Comparative I-001 — 70 150 72 rounded Example 9

On a silicon wafer, an undercoat material ODL-50 (Shin-Etsu Chemical Co., Ltd.) was coated and baked on a hot plate at 250° C. for 60 seconds to form an undercoat of 200 nm thick. A silicon-containing intermediate film material SHB-A940 (Shin-Etsu Chemical Co., Ltd.) was coated thereon and baked at 200° C. for 60 seconds to form a silicon-containing intermediate film of 35 nm thick. A photoresist composition was coated thereon and prebaked at 100° C. for 60 seconds to form a first photoresist film of 120 nm thick.

The first resist film thus formed was exposed to a pattern of five Y-direction lines having a width of 70 nm, a pitch of 140 nm and a length of 700 nm by means of an ArF excimer laser scanner S-307E (Nikon Corp., NA 0.85, σ 0.93-0.62, dipole illumination for Y direction lines) through a 6% halftone phase shift mask. Following exposure, the film was baked (PEB) at 100° C. for 60 seconds and developed with a 2.38 wt % TMAH solution for 30 seconds. A pattern of 70 nm lines in Y direction was formed and then baked at 190° C. for 60 seconds to induce crosslinking and deprotection. The line width of the first resist pattern was measured.

In Example 45, a second resist composition was coated on the first line pattern to form a second resist film of 50 nm thick. To define five X-direction lines intersecting perpendicularly the first pattern, the second resist film was exposed to a pattern of 5 X-direction lines having a line width of 70 nm, a pitch of 140 nm and a length of 700 nm by means of an ArF excimer laser scanner S-307E (Nikon Corp., NA 0.85, σ 0.93-0.62, dipole illumination for X direction lines) through a 6% halftone phase shift mask. This was followed by baking at 100° C. for 60 seconds and development in a 2.38 wt % TMAH solution for 30 seconds, yielding a dot pattern resulting from five X-direction lines and positive/negative reversal of overlapping Y-direction lines.

In Comparative Example 10, the resist film was exposed through a mask of the shape shown in FIG. 21 including five X-direction 70 nm lines at 140 nm pitches (on-mask size) and 70 nm dots. This was followed by baking at 100° C. for 60 seconds and development in a 2.38 wt % TMAH solution for 30 seconds, yielding a dot pattern formed from five X-direction 70 nm lines and 70 nm dots.

The size of lines and dots after development was measured under SEM. The results are shown in Table 7.

FIG. 21 shows the resist pattern after development in Example 45, and FIG. 22 shows the resist pattern after development in Comparative Example 10.

TABLE 7 1st 1st resist 2nd resist resist Resist formulation formulation line size dot size No. No. (nm) (nm) Dot shape Example 45 I-001 II-001 70 68 perpen- dicular Comparative I-001 — 70 20 rounded Example 10

On a silicon wafer, an undercoat material ODL-50 (Shin-Etsu Chemical Co., Ltd.) was coated and baked on a hot plate at 250° C. for 60 seconds to form an undercoat of 200 nm thick. A silicon-containing intermediate film material SHB-A940 (Shin-Etsu Chemical Co., Ltd.) was coated thereon and baked at 200° C. for 60 seconds to form a silicon-containing intermediate film of 35 nm thick. A photoresist composition was coated thereon and prebaked at 100° C. for 60 seconds to form a first photoresist film of 120 nm thick.

The first resist film thus formed was exposed by means of an ArF excimer laser scanner S-307E (Nikon Corp., NA 0.85, σ 0.93-0.62) through a 6% halftone phase shift mask to a pattern of Y-direction lines having a line width of 70 nm and a pitch of 140 nm under Y direction dipole illumination and then to a pattern of X-direction lines having a width of 70 nm at a pitch of 140 nm under X direction dipole illumination. Following exposure, the film was baked (PEB) at 100° C. for 60 seconds and developed with a 2.38 wt % TMAH solution for 30 seconds. A pattern of dots having a size of 50 nm and a pitch of 140 nm was formed and then baked at 190° C. for 60 seconds to induce crosslinking and deprotection.

A second resist composition was coated on the dot pattern and prebaked at 100° C. for 60 seconds to form a second photoresist film of 60 nm thick. Using an EB writing system HL-800D (Hitachi, Ltd.) at a HV voltage of 50 keV, a hole pattern was written between dots of the first resist pattern in a vacuum chamber.

Exposure was followed by baking at 100° C. for 60 seconds and development in a 2.38 wt % TMAH solution for 30 seconds. The first resist dot pattern was converted into a hole pattern through positive/negative reversal, and the second resist pattern was resolved as a hole pattern.

The size of holes after development was measured under SEM. The results are shown in Table 8.

FIG. 18 shows the resist pattern after development in Examples 46 to 49.

TABLE 8 Hole size Hole size resulting resulting from from 1st resist 2nd resist reversal of exposure of formulation formulation 1st resist 2nd resist No. No. (nm) (nm) Example 46 I-001 II-008 51 65 Example 47 I-001 II-009 52 60 Example 48 I-001 II-010 53 62 Example 49 I-001 II-011 52 63

While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Japanese Patent Application No. 2008-032668 is incorporated herein by reference.

Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims. 

1. A double pattern forming process comprising the steps of: coating a first chemically amplified positive resist composition onto a processable substrate, said resist composition comprising a resin comprising recurring units having an alkali-soluble group protected with an acid labile group which is eliminatable with acid, a photoacid generator capable of generating an acid upon exposure to high-energy radiation, and an organic solvent, and prebaking the resist composition to remove the unnecessary solvent to form a resist film, exposing the resist film to high-energy radiation in a first pattern of exposed and unexposed areas, post-exposure baking for causing the acid generated by the acid generator upon exposure to act on the acid labile groups on the resin whereby the acid labile groups on the resin in the exposed area undergo elimination reaction so that the resin in the exposed area becomes alkali soluble, and developing the exposed resist film with an alkaline developer to form a first positive resist pattern, treating the first resist pattern so as to eliminate the acid labile groups on the resin in the first resist pattern and to induce crosslinking in the resin to such an extent that the resin may not lose a solubility in an alkaline developer, for thereby endowing the first resist pattern with resistance to an organic solvent to be used in a reversal film-forming composition, coating a reversal film-forming composition thereon to form a reversal film, said reversal film-forming composition being a second chemically amplified positive resist composition comprising a resin comprising recurring units having an alkali-soluble group protected with an acid labile group which is eliminatable with acid, a photoacid generator capable of generating an acid upon exposure to high-energy radiation, and an organic solvent, and prebaking the second resist composition to remove the unnecessary solvent to form the reversal film, and exposing the reversal film to high-energy radiation in a second pattern of exposed and unexposed areas, post-exposure baking for causing the acid generated by the acid generator upon exposure to act on the acid labile groups on the resin whereby the acid labile groups on the resin in the exposed area undergo elimination reaction, and developing the exposed reversal film with an alkaline developer to form a second positive resist pattern, wherein the last step of developing the exposed reversal film with an alkaline developer to form a second resist pattern includes dissolving away the first resist pattern which has been converted to be soluble in the alkaline developer and achieving reversal transfer of the first resist pattern to the second resist pattern.
 2. The process of claim 1 wherein in the step of exposing, baking and developing to form a second resist pattern, exposure to the second pattern is performed between features of the first pattern to define the second resist pattern of spaces which are removable by alkaline development and located between spaces in the pattern resulting from reversal transfer of the first resist pattern, whereby repetitive patterns of lines and spaces are formed on the processable substrate.
 3. The process of claim 1 wherein in the step of exposing, baking and developing to form a second resist pattern, exposure to the second pattern is performed at a position spaced apart from the first resist pattern, whereby the second resist pattern is formed on the processable substrate apart from the pattern resulting from reversal transfer of the first resist pattern.
 4. The process of claim 1 wherein in the step of exposing, baking and developing to form a second resist pattern, exposure is performed to the second pattern that intersects the first resist pattern, whereby a second space pattern is formed as intersecting a space pattern resulting from reversal transfer of the first resist pattern.
 5. The process of claim 1 wherein in the step of exposing, baking and developing to form a second resist pattern, exposure is performed to the second pattern that intersects the first resist pattern, whereby a space pattern resulting from reversal transfer of the first resist pattern is formed in the second resist pattern.
 6. The process of claim 1 wherein the step of exposure to a first pattern and development forms a first dot pattern, and the step of exposure to a second pattern and development to form a second resist pattern includes exposure to a hole pattern between dots of the first dot pattern, and development to form a hole pattern between holes of a hole pattern resulting from reversal transfer of the first dot pattern.
 7. The process of claim 1 wherein in said first chemically amplified positive resist composition, the resin comprises recurring units having a lactone ring and recurring units of alicyclic structure having an alkali-soluble group protected with an acid labile group which is eliminatable with acid.
 8. The process of claim 7 wherein in said first chemically amplified positive resist composition, the resin comprises recurring units having a 7-oxanorbornane ring and recurring units having an alkali-soluble group protected with an acid labile group of alicyclic structure which is eliminatable with acid, and the step of treating the first resist pattern so as to eliminate the acid labile groups on the resin in the first resist pattern is performed by heating whereby elimination of acid labile groups and crosslinking of the resin simultaneously take place.
 9. The process of claim 7 wherein in said first chemically amplified positive resist composition, the resin comprises recurring units having the general formula (a):

wherein R¹ is hydrogen or methyl, R² is a single bond or a straight, branched or cyclic C₁-C₆ alkylene group which may have an ether or ester group, and which has a primary or secondary carbon atom through which it is linked to the ester moiety in the formula, R³, R⁴, and R⁵ are each independently hydrogen or a straight, branched or cyclic C₁-C₆ alkyl group, and “a” is a number in the range: 0<a<1.0.
 10. The process of claim 7 wherein the recurring units having an alkali-soluble group protected with an acid labile group which is eliminatable with acid are recurring units having the general formula (b):

wherein R⁶ is hydrogen or methyl, R⁷ is an acid labile group, and b is a number in the range: 0<b≦0.8.
 11. The process of claim 1 wherein in said second chemically amplified positive resist composition, the resin comprises recurring units having a lactone ring and recurring units having an alkali-soluble group protected with an acid labile group which is eliminatable with acid.
 12. The process of claim 11 wherein in said second chemically amplified positive resist composition, the recurring units having an alkali-soluble group protected with an acid labile group which is eliminatable with acid are recurring units having the general formula (c):

wherein R⁸ is hydrogen or methyl, R⁹ is an acid labile group, and c is a number in the range: 0<c≦0.8.
 13. The process of claim 1 wherein in said second chemically amplified positive resist composition, the resin comprising recurring units having an alkali-soluble group protected with an acid labile group which is eliminatable with acid is a polysiloxane compound.
 14. The process of claim 13 wherein in said second chemically amplified positive resist composition, the polysiloxane compound comprises structural units having the general formulae (1) and (2) and further comprises third structural units having the general formula (3):

wherein R¹⁰ is a C₃-C₂₀ monovalent organic group of straight, branched, cyclic or polycyclic structure which has a hydroxyl group on a carbon atom as a functional group, which has in total at least three fluorine atoms substituted on the carbon atoms bonded to the hydroxyl-bonded carbon atom, and which may contain a halogen, oxygen or sulfur atom in addition to the fluorine atoms, R¹¹ is a C₁-C₆ monovalent hydrocarbon group of straight, branched or cyclic structure, R¹² is a C₃-C₂₀ monovalent organic group of straight, branched, cyclic or polycyclic structure which has a carboxyl group protected with an acid labile protective group as a functional group, and which may contain a halogen, oxygen or sulfur atom in addition to the carboxyl group, R¹³ is as defined for R¹¹, R¹⁴ is a C₄-C₁₆ monovalent organic group which has a lactone ring as a functional group and which may contain a halogen, oxygen or sulfur atom in addition to the lactone ring, R¹⁵ is as defined for R¹¹, p is 0 or 1, q is 0 or 1, and r is 0 or
 1. 15. The process of claim 1 wherein the step of treating the first resist pattern for endowing the first resist pattern with resistance to an organic solvent to be used in a reversal film-forming composition includes heating at a higher temperature than in the prebaking and PEB steps.
 16. A double pattern forming process comprising the steps of: coating a first chemically amplified positive resist composition onto a processable substrate, said resist composition comprising a resin comprising recurring units having an alkali-soluble group protected with an acid labile group which is eliminatable with acid, a photoacid generator capable of generating an acid upon exposure to high-energy radiation, and an organic solvent, and prebaking the resist composition to remove the unnecessary solvent to form a resist film, coating a protective film-forming composition onto the resist film and heating to remove an unnecessary solvent to form a protective film, exposing the resist film to high-energy radiation in a first pattern of exposed and unexposed areas, post-exposure baking for causing the acid generated by the acid generator upon exposure to act on the acid labile groups on the resin whereby the acid labile groups on the resin in the exposed area undergo elimination reaction so that the resin in the exposed area becomes alkali soluble, and developing the exposed resist film with an alkaline developer to form a first positive resist pattern, treating the first resist pattern so as to eliminate the acid labile groups on the resin in the first resist pattern and to induce crosslinking in the resin to such an extent that the resin may not lose a solubility in an alkaline developer, for thereby endowing the first resist pattern with resistance to an organic solvent to be used in a reversal film-forming composition, coating a reversal film-forming composition thereon to form a reversal film, said reversal film-forming composition being a second chemically amplified positive resist composition comprising a resin comprising recurring units having an alkali-soluble group protected with an acid labile group which is eliminatable with acid, a photoacid generator capable of generating an acid upon exposure to high-energy radiation, and an organic solvent, and prebaking the second resist composition to remove the unnecessary solvent to form the reversal film, coating a protective film-forming composition onto the reversal film and heating to remove an unnecessary solvent to form a protective film, and exposing the reversal film to high-energy radiation in a second pattern of exposed and unexposed areas, post-exposure baking for causing the acid generated by the acid generator upon exposure to act on the acid labile groups on the resin whereby the acid labile groups on the resin in the exposed area undergo elimination reaction, and developing the exposed reversal film with an alkaline developer to form a second positive resist pattern, wherein the last step of developing the exposed reversal film with an alkaline developer to form a second resist pattern includes dissolving away the first resist pattern which has been converted to be soluble in the alkaline developer and achieving reversal transfer of the first resist pattern to the second resist pattern, thereby forming a pattern resulting from reversal transfer of the first resist pattern and the second resist pattern. 